POPULAR  HAND  BOOK 
FOR  CEMENT  AND 
CONCRETE  USERS 


A  COMPREHENSIVE  AND  POPULAR 
TREATISE  ON  THE  PRINCIPLES  INVOLVED 
AND  METHODS  EMPLOYED  IN  THE 
DESIGN  AND  CONSTRUCTION  OF  MODERN 
CONCRETE  WORK. 

A  Standard  Reference  Book  Covering  the  Uses  of  Plain 
and  Reinforced  Concrete.  Everything  of  Value  to  tbe 
Concrete  User  is  Given,  Including  Kinds  of  Cement 
Employed  in  Construction,  Concrete  Architecture, 
Inspection  and  Testing,  Waterproofing,  Coloring  and 
Painting,  Rules,  Tables,  Working  and  Cost  Data. 

By  MYRON  H.   LEWIS,   C.E. 

Author  of  "Examinations  for  Civil  Engineers,"  "  Waterproofing  of 
Concrete,"  Etc.,  Etc.,  and 

ALBERT   H.   CHANDLER,  C.E. 

Author  of  "  Materials  Employed  in  Construction,"  Etc. 


FULLY 


NEW  YORK 

THE    NORMAN    W.    HENLEY    PUBLISHING    COMPANY 

132  NASSAU  STREET 

1911 


v>v 


Copyrighted,  1911,  by 
The  Norman  W.  Henley  Publishing  Co. 


PREFACE 

ALTHOUGH  the  literature  of  cement  and  concrete  has  expanded 
enormously  during  the  past  few  years,  it  is,  nevertheless,  the  con- 
viction of  the  Publishers  that  there  is  still  a  place  for  a  semi-popular 
book  of  this  general  type.  Many  of  the  technical  works  are  either 
high  in  price  or  contain  a  great  deal  of  theory,  or  devote  so  many 
pages  to  academic  discussions  of  points,  not  yet  settled  by  current 
practice,  as  to  be  imperfectly  adapted  to  the  wants  of  the  non- 
technical reader. 

On  the  other  hand,  with  few  exceptions,  the  popular  books  on 
the  subject  contain  no  systematic  treatment  of  the  subject  of  design, 
and  fail  to  give  any  conception  of  the  costs  of  different  types  of 
construction. 

To  compile  material,  all  of  which  shall  possess  some  definite 
value;  to  explain  the  principles  of  design  and  methods  of  construc- 
tion in  concise  and,  so  far  as  possible,  non-technical  language;  to 
describe  the  variation  of  costs  for  different  kinds  of  concrete  work; 
to  give  the  reader  a  handbook  that  will  prove  interesting  as  well  as 
useful;  to  bring  home  the  great  economic  and  artistic  qualities  of 
concrete  as  a  building  material;  and  finally  to  help  in  producing  a 
better,  higher  grade  of  concrete  work:  these  are  the  criteria  which 
have  helped  to  shape  the  character  of  this  book,  criteria  difficult 
to  satisfy  and  impossible  of  complete  attainment.  Just  how  far 
these  purposes  have  been  carried  out  can  only  be  left  to  the  judg- 
ment of  the  readers  to  decide. 

In  the  preparation  of  the  text,  many  sources  of  information  have 
been  consulted,  including  the  standard  text  books  on  the  subject, 
the  published  transactions  of  the  American  Society  of  Civil  En- 
gineers, the  American  Society  for  Testing  Material,  and  the  National 
Association  of  Cement  Users;  also  recent  files  of  the  Engineering 
News,  Engineering  Record,  Engineering-Contracting,  Cement  Era, 
and  other  periodical  literature.  Particular  acknowledgment  is 
also  due  to  the  publications  of  the  Atlas  Portland  Cement  Co., 

[iii] 

268763 


Preface 

for  many  suggestions,  tables,  and  other  valuable  data.  The  bulle- 
tins of  the  Universal,  American,  Vulcanite,  and  Edison  Cement 
Companies  have  also  been  freely  drawn  upon. 

In  the  preparation  of  the  manuscript  many  suggestions  were 
also  received  from  individual  sources,  and  particular  acknowledg- 
ment is  due  to  the  following  engineers,  for  valuable  contributions 
and  advice: 

Mr.  Reginald  Van  Deerlin,  C.E.,  Chief  Engineer  Hennebique 
Construction  Co.;  Mr.  James  G.  Ray,  C.E.,  Consulting  Reinforced 
Concrete  Engineer;  Messrs.  Edmund  P.  Murray,  C.E.;  S.  B.  Balland, 
C.E.;  and  L.  B.  Manheimer. 

The  authors  would  also  be  glad  to  receive  and  to  acknowledge, 
in  future  editions,  further  suggestions,  criticisms,  cost  data,  or 
examples  of  recent  practice  from  any  of  their  readers. 

They  especially  solicit  cost  data  in  connection  with  all  kinds  of 
concrete  work,  and  will  acknowledge  and  publish  same  in  future 
editions  of  this  book. 

MYRON  H.  LEWIS, 
February,  1911.  ALBERT  H.  CHANDLER. 


[iv] 


CONTENTS 


CHAPTER  I 

INTRODUCTORY  PAGE 

The  Renaissance  of  Concrete. — The  Concrete  Age. — Concrete  Architecture. — 

Concrete  Literature. — The  Future  of  Concrete,      .         .        ...         .  1-4 

CHAPTER   II 

KINDS   OF    CEMENT   AND   HOW   THEY   ARE   MADE 

Common  Lime. — Lime  Mortar. — Hydraulic  Lime. — Puzzuolana. — Hydraulic 
Cements. — Theory  of  Setting. — How  Natural  Cement  is  Made. — How 
Portland  Cement  is  Made. — White  Portland  Cement. — Slag  Cements. — 
Plaster  Cements.— Choice  of  Cements. — How  Portland  Cement  Comes  5-17 

CHAPTER   III 

PROPERTIES,    TESTING,    AND   REQUIREMENTS    OF   HYDRAULIC   CEMENTS 

Description  of  Tests. — How  the  Tests  Are  Made. — Standard  Requirements 

for  Natural  and  Portland  Cements,       .         .       -.      '  .         .        .         .       18-25 

CHAPTER   IV 

CONCRETE   AND    ITS    PROPERTIES 

What  Concrete  Is. — Kinds  of  Concrete. — Function  and  Effect  of  the  Cement. 
— Aggregates,  Water,  Chemicals,  Weather  Conditions,  Gases,  Sewage, 
etc. — Laws  of  Strength  and  Permeability, 26~35 

CHAPTER   V 

SAND,    BROKEN   STONE,    AND   GRAVEL  FOR   CONCRETE 

Selection  of  Sand. — Tests  for  Sand. — Washing  Sand. — Mixture  of  Bank 

Sand  and  Gravel.— Broken  Stone.— Gravel, 36-41 

CHAPTER   VI 

HOW   TO    PROPORTION   THE   MATERIALS 

Nature  of  the  Problem. — Voids  in  Concrete. — Methods  of  Proportioning. — 

Tables  for  Proportioning, 42-46 

[v] 


Contents 

CHAPTER  VII 

HOW  TO  MIX  AND  PLACE  CONCRETE  PAGE 

Methods  of  Mixing. — How  to  Mix  by  Hand. — Materials  Required  for  Two- 
Bag  Batch. — Mixing  by  Machine. — Placing  the  Concrete. — Protection 
of  Concrete  After  Placing. — -Placing  Concrete  Under  Water,  .  .  47-63 

CHAPTER   VIII 

FORMS  FOR  CONCRETE  CONSTRUCTION 

Kinds  of  Forms. — Pressure  of  Concrete  on  Forms. — Dressing  and  Lubrica- 
tion of  Forms. — Design  of  Forms. — Removing  Forms. — Cost  of  Forms  64-77 

CHAPTER   IX 

THE  ARCHITECTURAL   AND   ARTISTIC  POSSIBILITIES   OF   CONCRETE 

A  New  Style  of  Architecture, 78-81 

CHAPTER   X 

CONCRETE   RESIDENCES 

The  Use  of  Concrete  for  Residences. — Best  Method  of  Obtaining  Architec- 
tural Effects. — Stucco  and  Reinforced  Concrete  for  Residences. — The 
Edison  Poured  Concrete  House. — Cost  of  Different  Types  of  Resi- 
dences Compared,  .  .  .  .  .  .  .  .  .  82-89 

CHAPTER   XI 

MORTARS,    PLASTERS,    AND    STUCCOS,    AND    HOW   TO   USE   THEM 

The  Art  of  Stuccoing. — Lime  Mortars  and  Plasters. — Interior  Plasters  and 
Plastering. — Gypsum  Plasters. — Portland  Cement  Plasters  or  Stucco. — 
Exterior  Lathing  and  Plastering. — Application  of  Stucco  to  Stone. — 
Stucco  on  Brick. — Stucco  on  Concrete. — Quantities  of  Materials  for 
Stucco, 90  105 

CHAPTER   XII 

THE   ARTISTIC   TREATMENT    OF    CONCRETE    SURFACES 

Imperfections  in  Concrete  Surfaces. — Methods  of  Finishing  Surfaces. — Spad- 
ing.— Stucco. — Mortar  Facing. — Grouting. — Scrubbing  and  Washing. 
— Etching. — Tooling. — Selected  Aggregates. — Tinting  and  Coloring. — 
Panelling. — Mosaics,  Carving,  etc.,  Prevention  of  Cracking  and  Crazing  106-117 

CHAPTER   XIII 

CONCRETE   BUILDING    BLOCKS      - 

Advantages  and  Disadvantages  of  Concrete  Blocks. — Materials  for  Concrete 
Blocks. — Types  of  Blocks. — Block  Machines. — Making  the  Blocks. — 
Coloring  the  Blocks. — Waterproofing  the  Blocks. — Building  Details. — 
Cost  of  Blocks. — Objections  to  Concrete  Blocks  and  Remedies  for  Same. 
— Table  of  Concrete  Block  Data. — Concrete  Tiles,  etc. — Specifications 

for  Concrete  Blocks, .         .         .     *   .  118-138 

[vi] 


Contents 

CHAPTER   XIV 

THE  MAKING   OF   ORNAMENTAL  CONCRETE  PAGE 

Methods     Employed. — Modelling. — Moulding. — Wooden,     Metal,    Plaster, 

Glue,  and  Sand  Moulds,       .  .         .  .         .         .         .  139-149 

CHAPTER  XV 

CONCRETE   PIPES,    FENCE   POSTS,    ETC. 

Advantages  of  Concrete  Pipes. — Moulds,  Machines,  and  Manufacture  of  Re- 
inforced Concrete  Pipes. — Concrete  Tile,  Data,  and  Costs. — Advan- 
tages of  Concrete  Fence  Posts. — Moulds,  Machines,  and  Manufacture. — 
Reinforcement  for  Fence  Posts. — Fastening  Fence  to  Posts. — Quantity 
of  Materials  for  Fence  Posts,  . 150-164 

CHAPTER  XVI 

ESSENTIAL   FEATURES   AND    ADVANTAGES   OF   REINFORCED   CONCRETE 

Essential  Features. — Materials  Employed,     .......    165-168 

CHAPTER   XVII 

HOW  TO  DESIGN  REINFORCED  CONCRETE  BEAMS,  SLABS,  AND  COLUMNS 
Nature  of  the  Problem. — Kinds  of  Stresses. — Rules  for  Designing  Beams. — 
Rules  for  Designing   Slabs. — Tables  for  Designing. — Solution  of  Ex- 
amples.—Summary  of  Procedure   in  Design. — Design   of  Reinforced 
Concrete  Columns. — Examples  and  Solution,       .....   169-193 

CHAPTER  XVIII 

EXPLANATION    OF    THE    THEORY    OF    THE    DESIGN    OF    REINFORCED   CONCRETE   BEAMS 

AND    SLABS 

Explanation  of  the  Theory  of  the  Design  of  Reinforced  Concrete  Beams  and 
Slabs,    and    General    Specifications    for    Reinforced    Concrete. — The 
Mechanics  of  the  Beam. — Stresses  and    Moments. — Derivation  of  For- 
mulas,.   .         .       --_       .  .  •       .         .         .         .         .         .         .  194-212 

CHAPTER   XIX 

SYSTEMS    OF   REINFORCEMENT    EMPLOYED 

Systems  of  Reinforcement  Employed. — Different  Forms  of  Rods  and  Bars. — 

Special  Fabrics  and  Types  of  Reinforcement, 213-222 

CHAPTER  XX 

REINFORCED    CONCRETE    IN    FACTORY    AND    GENERAL    BUILDING    CONSTRUCTION 
Advantages  of  Reinforced   Concrete  in   Building   Construction. — Practical 
Details   of   Construction. — Slabs,    Columns,    Floors,    Loads,    Walls. — 
Roofs. — Attaching  Machinery, 223-232 

[vii] 


Contents 

CHAPTER   XXI 

CONCRETE   IN   FOUNDATION    WORK  PAGE 

Importance  of  Foundations. — Loads  on  Foundations. — Methods  of  Securing 
Good  Foundations. — Essential  Requirements  in  Construction. — Con- 
crete in  Foundations. — Reinforced  Concrete  Piles. — Caissons. — Cribs  233-244 

CHAPTER   XXII 

CONCRETE  RETAINING   WALLS,    ABUTMENTS,   AND   BULKHEADS 
Design   of  Walls  in   General. — Methods  of  Failure. — Kinds  of  Retaining 
Walls. — Design    of    Gravity    Walls. — Reinforced    Concrete    Walls. — 
Details     of     Construction. — Foundations. — Abutments. — Bulkheads. — 
Appearance  of  Walls. — Tables  for  Design  of  Walls,      ....  245-260 

CHAPTER  XXIII 

CONCRETE   ARCHES   AND   ARCHED    BRIDGES 

Definitions. — Parts  of  an  Arch. — Methods  of  Failure. — Design  of  an  Arch. — 
Abutments  and  Piers. — Reinforced -Concrete  Arches. — Arch  Bridges. — 
Arch  Centres. — Concreting  the  Arch,  .......  261-272 

CHAPTER  XXIV 

CONCRETE   BEAM   AND   GIRDER   BRIDGES 

Advantages  of  Concrete  Bridges. — Kinds  of  Girder  Bridges. — Reinforced 
Concrete. — Trusses. — Viaducts. — Concrete  Floors. — Abutments. — Cen- 
tring.— Depositing  Concrete. — Surface  Finish,  .  .  .  .  .  273-280 

CHAPTER   XXV 

CONCRETE  IN   SEWERAGE  AND  DRAINAGE  WORKS 

Advantages  of  Concrete  for  Sewers. — Forms  of  Sewers. — Combined  and 
Separate  Systems. — Dimensions  of  Sewers. — Construction  of  Sewers 
and  Conduits. — Quantity  of  Flow. — Culverts  and  Drains. — Types  of 
Culverts. — Imperviousness  of  Sewers  and  Conduits. — Tables  of  Dimen- 
sions for  Culverts,  ,.-.., 281-293 

CHAPTER   XXVI 

CONCRETE  TANKS,  DAMS,  AND  RESERVOIRS 

Uses  of  Concrete  Tanks. — How  to  Build  Tanks. — Reinforcement  for  Tanks. 
— Concrete  Dams. — Small  Reinforced  Concrete  Dams. — Concrete 
Reservoirs, 294-304 

CHAPTER   XXVII 

CONCRETE   SIDEWALKS,    CURBS,    AND   PAVEMENTS 

Advantages  of  Concrete  Sidewalks. — Materials,  Equipment,  and  Forms. — 
Construction  of  the  Sidewalk. — Coloring  and  Protection. — Tables  of 
Dimensions  and  Materials  Required. — Concrete  Curbs  and  Gutters. — 
Concrete  Roads  and  Pavements.— Table  of  Offsets  for  Crowning  Roads  305-316 

[  viii  ] 


Contents 

CHAPTER  XXVIII 

CONCRETE   IN   RAILROAD    CONSTRUCTION  PAGE 

Foundations  and  Retaining  Walls. — Bridges  and  Trestles. — Train  Sheds  and 
Platforms. — Signal  Towers. — Power  Houses. — Shops  and  Warehouses. — 
Coal  and  Sand  Pockets. — Ash  Plants. — Round  Houses. — Turntables, 
Pits,  Tank  Supports,  and  Bumping  Posts. — Concrete  Ties  and  Road- 
bed.— Posts  and  Fences. — Telegraph  Poles. — Tunnels. — Docks. — Reser- 
voirs.— Elevators,  .  .  .  .  .  .  ...  .  .  .  317-331. 

CHAPTER   XXIX 

THE   UTILITY   OF   CONCRETE   ON   THE   FARM 

Advantages  of  Concrete  for  the  Farmer. — Concrete  Types  Found  on  the 
Farm. — Posts. — Troughs. — Tanks. — Farm  Drainage. — Cisterns. — Cess 
Pools. — Stalls. — Silos. — Miscellaneous. — Useful  Hints  for  the  Farmer  332-343 

CHAPTER  XXX 

THE  WATERPROOFING   OF   CONCRETE   STRUCTURES 

The  Necessity  for  Waterproofing. — Modern  Methods  of  Waterproofing. — 
General  Conditions  of  the  Work. — Principles  to  be  Followed. — The 
Membrane  Method  in  Detail.— The  Integral  Method  in  Detail.— Water- 
proofing by  Means  of  Surface  Coatings. — Tabular  Outline  of  Modern 
Waterproofing  Processes,  .  .  .  •  •  •  •  •  344~374 

CHAPTER   XXXI 

GROUT,  OR  "LIQUID  CONCRETE"  AND  ITS  USES 
Preparing  and  Mixing  Grout. — Mixing  Machines. — Various  Uses  of   Grout  375-385 

CHAPTER  XXXII 

INSPECTION  OF  CONCRETE   WORK — A   SUMMARY  OF   ESSENTIAL  RULES   AND   PRINCIPLES 
OF  CONSTRUCTION,   FOR  SECURING   GOOD   CONCRETE  WORK 

The  Work  of  the  Inspector. — Inspection  of  the  Cement,  Sand,  and  Aggre-' 
gates. — Proportioning  and  Mixing. — Inspection  of  Forms,  Reinforce- 
ment and  Placing  Concrete. — Rules  for  Removing  Forms. — Rules  for 
Surface  Finish.— Rules  for  Blocks,  Piles,  and  Castings,  ....  386-399 

CHAPTER   XXXIII 

COST   OF    CONCRETE    WORK 

General  Cost  of  Main  Classes  of  Work. — Elements  of  Cost. — Cost  of  Mate- 
rials.— Cost  of  Mixing. — Cost  of  Placing.— General  Expenses. — Sum- 
mary of  Costs. — Cost  of  Mortar. — Actual  Examples  of  Cost. — Building 
Blocks. — Paving. — Removing  Efflorescence. — Stucco. — Forms. — Cost  of 
Buildings  in  Terms  of  Cubical  Contents. — Cost  of  Residences. — Cost  of 
Sewers. — Concrete  Pipes. — Bridge  Piers  and  Bridges. — Piles. — Trestles, 
Sidewalks,  Curbs,  and  Gutters. — Fence  Posts. — Poles. — Roofs. — Tunnel 
Lining. — Waterproofing. — Cost  of  Concrete  Dams,  ....  400-421 

[ix] 


SECTION  I 
PRELIMINAKY   INFORMATION 

FOR   THE 

CEMENT  AND  CONCEETE  USEK 


CHAPTER  I 

INTRODUCTORY 

The  Renaissance  of  Concrete. — The    Concrete  Age. — Concrete  Architecture. — Con- 
crete Literature. — The  Future  of  Concrete. 

The  Renaissance  of  Concrete. — The  history  of  concrete  is  a 
history  of  an  ancient  and  highly  developed  art,  long  lost  and  for- 
gotten during  the  dark  centuries  of  the  middle  ages,  and  having  a 
new  awakening  and  renaissance  nearly  two  thousand  years  later. 
Some  of  the  costly  and  magnificent  structures  of  concrete  built  by 
the  Romans  during  the  period  of  their  supremacy  still  remain  as 
time-defying  evidence  of  their  great  skill  as  constructors,  and  as 
monuments  to  the  utilitarian  character  of  their  art.  As  a  seed 
planted  in  an  arid  soil  springs  to  life  at  the  first  visiting  of  rain,  so 
has  concrete  been  born  anew  in  the  twentieth  century  when  the  state 
of  industrial  and  constructive  art  became  favorable  to  its  develop- 
ment ;  and  with  such  new  life,  it  has  reached  a  much  higher  state  of 
development,  and  attained  a  wider  application  and  a  more  per- 
manent place  in  our  civilization  than  was  ever  dreamed  of  by  our 
Roman  predecessors. 

How  broadly  concrete  has  entered  into  our  modern  lives  has 
been  well  put  by  Kerwin  in  an  address  before  the  National  Associa- 
tion of  Cement  Users  in  the  following  words: 

The  Concrete  Age. — "Our  ancestors  progressed  from  the  Stone 
Age  to  the  Iron  Age;  we  seem  to  be  passing  from  the  Steel  Age  to 
the  Cement  Stone  or  Concrete  Age.  We  tread  on  concrete  walks, 
travel  in  concrete  subways,  over  concrete  bridges,  live  and  work  in 


Handbook  For  Cement  and  Concrete  Users 

concrete  buildings,  store  our  grain  in  concrete  elevators,  draw  our 
water  from  concrete  reservoirs  and  cisterns,  sanitate  our  cities  with 
concrete  sewers,  and  are  finally  buried  in  concrete  cases  deposited 
in  concrete  tombs,  and  our  numerous  virtues  are  inscribed  on 
concrete  monuments." 

It  is  certainly  well  that  this  development  has  come  at  a  time 
when  our  rapidly  disappearing  forests  have  given  serious  alarm  as 
to  our  future  supply  of  timber,  and  what  a  boon  the  concrete  in- 
dustry will  be  to  humanity  and  civilization  throughout  the  world, 
cannot  be  appreciated  so  well  to-day  as  it  will  years  hence  when  the 
supply  of  timber  has  fallen  far  below  the  normal  requirements. 

Mr.  Andrew  Carnegie  is  probably  best  known  as  a  philanthropist 
interested  in  education  and  free  libraries,  but  it  should  not  be  for- 
gotten that  he  is  also  probably  the  greatest  living  authority  on 
questions  relating  to  the  production  of  steel,  and  that  any  statement 
made  by  him  relating  to  the  position  of  steel  should  carry  great 
weight. 

At  the  recent  conference  of  governors  and  scientists  at  the  White 
House,  Washington,  which  was  held  under  the  chairmanship  of  ex- 
President  Roosevelt,  there  was  a  discussion  on  the  conservation  of 
the  natural  resources  of  the  United  States,  in  the  course  of  which 
Mr.  Carnegie,  speaking  of  iron,  said : 

"The  next  great  use  of  iron  is  in  construction,  especially  of 
buildings  and  bridges.  Fortunately  the  use  of  concrete,  simple 
and  reinforced,  is  already  reducing  the  consumption  of  structural 
steel.  The  materials  for  cement  and  concrete  abound  in  every  part 
of  the  country;  and  while  the  arts  of  making  and  using  them  are 
still  in  their  infancy,  the  products  promise  to  become  superior  to 
steel  and  stone  in  strength,  durability  and  convenience,  and  economy 
and  use." 

For  a  great  steelmaker  to  announce  his  conviction  that  concrete 
promises  to  become  superior  to  steel  and  stone  in  strength,  dur- 
ability, convenience,  and  economy,  is  indeed  a  matter  that  should 
claim  the  attention  of  our  economists. 

The  period  of  the  most  rapid  development  of  the  concrete  in- 
dustry was  inaugurated  when  the  value  of  the  combination  of  steel 
and  concrete  was  recognized.  This  combination,  fortunate  as 
Carnegie  says,  opened  up  a  field  of  unlimited  usefulness  and  gave 


Introductory 

to  our  civilization  a  new  material,  possessing  nearly  all  the  virtues 
of  the  materials  hitherto  employed  in  construction  and  few  of  their 
defects,  and  so  superior  in  strength,  heat-resisting,  and  other  qualities 
as  to  make  its  universal  adoption  a  matter  of  certainty. 

Concrete  Architecture. — It  was  at  first  these  utilitarian  qualities 
that  were  recognized  and  made  use  of  by  engineers,  but  another 
great  step  forward  was  taken  when  the  artistic  and  aesthetic  possi- 
bilities of  concrete  were  recognized  by  architects  and  builders. 

The  recognition  thus  accorded  has  given  the  latter  what  it  had 
sought  almost  in  vain  for  centuries — a  new  style  of  architecture; 
a  style  entirely  free  from  the  hereditary  tendencies  of  the  ancient 
and  mediaeval  styles,  and  which  could  be  rendered  possible  only  by 
the  introduction  of  a  new  material,  possessing  properties  entirely 
distinct  from  those  whose  possibilities  had  been  studied  and  studied 
for  ages.  The  essential  features  of  the  new  style,  which  will  be 
distinctive  of  the  early  years  of  the  present  century,  are  pointed  out 
under  the  section  on  Concrete  Architecture. 

Concrete  Literature. — Another  potent  influence  in  the  modern 
development  of  concrete  work  is  the  broad-mindedness  and  liber- 
ality of  the  manufacturers  of  cement  and  cement  products,  in  bring- 
ing home  to  the  public  the  many  marked  advantages  and  possible 
uses  of  cement  and  concrete.  Foremost  in  this  class  are  the  many 
publications  of  the  Atlas  Portland  Cement  Co.,  the  excellence  of 
which,  from  a  typographical,  authoritative,  and  readable  standpoint, 
cannot  be  overestimated,  and  in  the  preparation  of  this  volume 
the  Authors  have  availed  themselves  of  the  Company's  kindness  in 
permitting  them  to  extract  a  number  of  excellent  tables  and  illustra- 
tions from  their  various  publications. 

The  excellent  series  of  bulletins  issued  by  the  American  Associa- 
tion of  Portland  Cement  Manufacturers  are  another  source  by 
means  of  which  a  wide  dissemination  of  knowledge  of  the  possi- 
bilities of  cement  has  been  effected,  and  from  which  the  Authors 
have  drawn  some  valuable  material. 

A  great  deal  has  been  contributed  to  the  industry  by  the  numer- 
ous organizations  formed  for  the  promotion  of  knowledge  on  cement 
and  concrete  work.  The  cement  shows  held  in  various  parts  of 
the  country  during  the  past  few  years  have  also  given  an  acceleration 
to  the  development  of  the  industry.  The  proceedings  of  the 

[3] 


Handbook  for  Cement  and   Concrete  Users 

National  Association  of  Cement  Users  at  their  Conventions  during 
these  shows  have  been  brimful  of  new  ideas  and  their  annual 
bulletins  have  preserved  the  best  of  these  for  future  reading  and 
study.  The  Authors  have  also  used  these  books  in  drawing  material 
for  this  volume. 

The  cement  and  concrete  press  of  the  country  have  done  a 
great  work  in  spreading  widely  the  gospel  of  concrete,  defending 
it  against  attacks  by  its  older  but  worried  competitors  and  keeping 
the  building  public  informed  of  the  latest  developments  in  this 
rapidly  growing  field. 

The  Future  of  Concrete. — Many  other  influences  have  con- 
tributed to  the  growth  of  the  concrete  industry  and  these  are  dis- 
cussed in  the  appropriate  sections  of  the  book.  No  doubt  the 
future  will  witness  many  new  contributing  causes,  and  there  is 
every  reason  for  believing  that  the  future  holds  out  the  most  brilliant 
prospect  for  this  apparently  homely  but  invaluable  building  material. 

We  can  prophesy  that  future  ages  will  be  grateful  to  the  present 
one  for  the  renaissance  of  concrete,  for  with  it,  as  time  goes  on,  will 
come  more  beauty  in  our  structures,  more  healthful  conditions  of 
life  resulting  from  the  sanitary  nature  of  the  material,  more  buildings 
of  historic  fame,  and  temples  far  more  creditable  to  our  architecture; 
for  when  the  present  monumental  structures  of  timber,  steel,  and 
iron  shall  have  succumbed  to  the  corroding  hand  of  time,  our 
concrete  structures,  built  of  more  enduring  stuff,  will  still  live  and 
endure  to  tell  the  story  of  the  rebirth  of  concrete  in  the  twentieth 
century. 


Ul 


CHAPTER  II 

.KINDS  OF  CEMENT  AND  HOW  THEY  ARE  MADE 

Common  Lime. — Lime  Mortar. — Hydraulic^Lime. — Puzzuolana. — Hydraulic  Cements. 
— Theory  of  Setting. — How  Natural  Cement  is  Made. — How  Portland  Cement  is 
Made. — White  Portland  Cement. — Slag  Cements. — Plaster  Cements. — Choice  of 
Cements. — How  Portland  Cement  Comes. 

LIMES  and  cements  which  are  used  to  unite  brick,  stone,  and 
concrete  are  nearly  all  derived  from  the  roasting  of  pure  and  impure 
limestones  and  can  be  grouped  into  three  classes. 

1.  Common,  fat,  or  quick  lime,  which  hardens  in  air. 

2.  Hydraulic  lime,  which  hardens  in  air  when  slaked,  and  sets 
on  the  addition  of  water,  either  when  exposed  to  the  air  or  sub- 
merged. 

3.  Hydraulic  cement,  which,  when  water   is  added,  sets  either 
in  air  or  under  water  and  acquires  great  strength. 

Common  Lime. — Common  lime  is  a  combination  of  calcium 
and  oxygen,  and  is  obtained  by  driving  off  carbon  dioxide  gas  from 
limestone.  When  it  contains  not  more  than  about  12  per  cent  of 
impurities,  it  has  the  property  of  absorbing  water  with  great  avidity. 

The  process  of  absorption  of  water  is  accompanied  by  a  great 
rise  of  temperature,  by  the  evolution  of  hot  and  slightly  caustic 
vapors,  and  finally  by  the  reduction  of  the  lime  to  a  powder.  The 
powder  thus  formed  is  called  slaked  lime,  and  the  operation  of 
adding  water  to  quicklime  is  thus  known  as  slaking. 

Good  lime  comes  in  hard  lumps,  and  contains  but  little  dust. 
When  slaked,  its  bulk  increases  from  2^  to  3^  times  its  original 
volume,  while  the  amount  of  water  which  it  will  absorb  is  nearly 
1/4  of  its  weight. 

When  just  enough  water  is  added  to  lime  to  cause  it  to  slake,  it 
forms  a  powder;  when  more  water  is  added  it  forms  a  paste.  Lime 
mortar  is  made  by  mixing  the  paste  of  slaked  lime  with  sand,  and 
is  extensively  used  in  the  building  trades. 

The  ordinary  method  of  slaking  lime  consists  in  first  placing 
the  lumps  in  a  layer,  6  or  8  inches  deep,  in  either  a  water-tight 

[5] 


Handbook  for  Cement  and  Concrete  Users 

or  a  basin  formed  in  the  sand,  and  then  pouring  upon  the  lumps  a 
quantity  of  water  equal  to  2  %  to  3  times  the  volume  of  the  lime. 

In  slaking  lime,  it  is  important  "that  enough  water  be  added, 
but  not  too  much.  If  too  much  is  added,  the  slaked  lime  is  reduced 
to  a  semi-fluid  condition.  If  not  enough,  the  addition  of  water 
during  the  slaking  chills  the  lime  and  renders  it  granular  and  lumpy. 
Covering  the  bed  of  lime  with  a  tarpaulin  or  with  a  layer  of  sand 
retains  the  heat  and  accelerates  the  slaking.  All  the  lime  necessary 
for  any  required  quantity  of  mortar  should  be  slaked  at  least  one 
day  before  it  is  incorporated  with  the  sand. 

Lime  Mortar. — The  paste  of  slaked  lime  is  mixed  with  from 
2j  to  3  volumes  of  sand  to  form  mortar.  Sand  is  used  to  reduce 
the  cost,  and  to  prevent  the  mortar  from  cracking.  It  also  causes 
the  lime  paste  to  spread  out  in  thin  films  around  each  grain  and 
thus  enables  it  to  harden.  Too  much  sand  should  not,  however, 
be  used,  as  it  tends  to  make  the  mortar  porous. 

The  hardening  of  lime  mortar  is  a  double  process  and  consists  of : 

1.  The  formation  of  crystals,  as  the  lime  gradually  dries  out. 

2.  The  slow  formation  of  carbonate  of  lime  or  limestone  through 
the  absorption  of  carbonic  acid  from  the  air. 

Lime  mortar  acquires  strength  only  by  the  absorption  of  carbonic 
acid.  This  is  a  slow  process,  and  does  not  take  place  unless  there 
is  a  free  circulation  of  air  to  carry  the  carbonic  acid  to  the  mortar. 
Hence  in  a  thick  wall,  lime  mortar  will  harden  only  after  the  lapse 
of  years  or  perhaps  never. 

Lime  mortar  can  neither  harden  nor  acquire  strength  when 
used  under  water  or  in  soil  that  is  constantly  wet,  because  slaked 
lime  cannot  crystallize  until  it  dries  out,  and  it  cannot  absorb 
carbonic  acid  when  submerged. 

Lime  mortar  is  also  weak,  because  the  absorption  of  carbonic 
acid  is  a  very  slow  process,  especially  in  the  interior  of  the  mass. 
The  surface  hardens,  but  the  interior  remains  soft.  The  carbonic 
acid  penetrates  about  i/io  of  an  inch  into  the  joint  the  first  year, 
forming  a  skin  or  film  which  opposes  its  further  absorption,  except 
at  a  decreasing  ratio.  So  slow  is  its  penetration  after  the  surface 
film  has  formed,  that  the  Scotch  have  a  proverb,  "  When  a  hundred 
years  are  past  and  gane,  then  gude  mortar  turns  into  stane." 

Hydraulic  Lime. — Hydraulic  lime  is  obtained  by  roasting  a 

[6] 


Kinds  of  Cement  and  How  They  are  Made 

limestone  which  contains  from  15  to  25  per  cent  of  silica  and 
alumina. 

In  hydraulic  limes,  there  are  two  principal  constituents: 

i.  Free  slaked  lime;  2.  Lime  chemically  combined  with  silica 
and  alumina. 

When  a  limestone  containing  silica  and  alumina  is  roasted, 
the  two  latter  elements  combine  with  a  portion  of  the  lime,  forming 
silicates  and  aluminates  of  lime.  The  rest  remains  as  free  lime 
in  an  uncombined  state. 

When  treated  witri  water  the  free  lime  is  slaked.  The  action  is, 
however,  retarded  by  the  silicates  and  aluminates,  and  is  much  less 
energetic  than  that  of  fat  lime.  When  mixed  with  water  to  form  a 
paste,  hydraulic  lime  can  be  used  in  the  same  way  as  common  lime. 
When  so  treated  the  free  slaked  lime  in  its  composition  dries, 
hardens,  and  slowly  absorbs  carbonic  acid  on  exposure  to  the  air. 
The  free  lime  also  causes  it  to  crack  when  used  without  sand,  but 
the  swelling  and  cracking  are  much  less  pronounced  than  in  the 
case  of  fat  limes. 

When  used  in  water  or  in  damp  places,  the  actions  of  common 
and  hydraulic  limes  differ  greatly  from  each  other.  While  common 
lime  remains  soft,  hydraulic  lime  sets  with  more  or  less  rapidity. 
Its  property  of  setting  is  due  to  the  crystallization  of  the  combined 
lime,  the  free  lime  being  inert  if  not  actually  washed  away  by  the 
action  of  the  water.  The  crystallization  of  the  combined  lime 
and  consequent  hardening  of  the  mortar  is  identical  with  the  re- 
actions which  take  place  in  hydraulic  cement.  Hydraulic  lime  is, 
however,  much  inferior  to  cement  in  respect  to  reliability  and 
strength,  and  is  in  consequence  but  little  used  in  the  United  States. 

Hydraulic  lime  is  commonly  slaked  at  the  manufactory  and 
shipped  in  the  form  of  powder.  It  may  be  kept  without  injury  in 
this  form  if  covered  and  protected  from  the  air. 

Puzzuolana. — The  term  "Puzzuolana"  is  commonly  applied  to 
a  class  of  materials  which,  when  made  into  a  mortar  with  either  fat 
or  feebly  hydraulic  lime,  impart  to  the  lime  the  property  of  setting 
on  the  addition  of  water.  This  set  will  take  place  both  when  sub- 
merged and  when  left  exposed  to  the  air. 

Puzzuolana  is  a  material  of  volcanic  action,  which  derives  its 
name  from  Pozzuoli,  a  city  of  Italy  near  the  foot  of  Mount  Vesuvius, . 

[7] 


Handbook  for  Cement  and  Concrete  Users 

where  its  properties  were  first  discovered.  It  was  extensively  used 
by  the  Romans  in  their  hydraulic  constructions,  being  pulverized 
and  mixed  with  slaked  lime  and  a  small  amount  of  sand  for  the 
formation  of  hydraulic  mortar. 

HYDRAULIC  CEMENTS 

Hydraulic  cements,  which  are  ,the  kinds  used  in  concrete  con- 
struction, may  be  classified  according  to  the  method  of  manu- 
facture, under  three  general  headings: 

1.  Portland  cements. 

2.  Natural  cements. 

3.  Puzzolan  or  slag  cements. 

The  term  Portland  cement  is  commonly  used  to  designate 
hydraulic  cement  formed  by  burning  a  mixture  of  limestone  and 
clay  in  proper  proportions  to  the  point  where  they  begin  to  fuse  or 
melt.  The  materials  then  combine  chemically  and  form  a  hard 
clinker,  which  when  ground  to  a  powder  acquires  the  property  of 
setting  under  water. 

The  term  Natural  cement  is  commonly  employed  to  designate 
a  large  number  of  widely  varying  products  formed  by  burning 
natural  rock  without  pulverization  or  the  admixture  of  other  ma- 
terials. When  thus  roasted  a  clinker  is  formed,  which  when  ground 
to  a  powder  acquires  the  property  of  setting  under  water.  The 
materials  used  for  this  purpose  are  limestones  which  contain  silica, 
alumina,  and  iron  oxide  in  quantities  greater  than  would  be  needed 
for  Portland  cement. 

There  are  many  brands  of  natural  cement.  Perhaps  the  most 
familiar  are  Rosendale,  Utica,  Akron,  and  Roman  cements. 

Puzzolan  or  Slag  Cements  are  formed  by  the  admixture  of 
slaked  lime  with  ground  blast-furnace  slag.  The  slag  has  ap- 
proximately the  composition  of  a  hydraulic  cement,  but  lacks  a 
proper  proportion  of  lime  to  give  it  the  property  of  setting  under 
water.  These  cements  are  sometimes  called  puzzolana  cements, 
on  account  of  their  resemblance  to  the  Puzzolana  of  Italy. 

The  Setting  of  Cement. — When  cement  powder  is  mixed  with 
water  to  a  plastic  condition,  a  chemical  action  takes  place  which 
causes  the  materials  to  solidify  or  set. 

[81 


Kinds  of  Cement  and  How  They  are  Made 

The  setting  of  cement,  according  to  the  general  theory,  is  prob- 
ably due  to  the  action  of  water  in  releasing  the  lime  from  its  chemical 
union  with  alumina.  This  free  lime,  the  moment  that  it  is  liberated, 
is  in  solution  in  the  water,  but  owing  to  the  rapidity  with  which  it 
is  liberated  the  water  soon  becomes  supersaturated  with  hydrated 
lime,  and  the  latter  crystallizes  out  in  a  network  of  crystals  which 
binds  the  particles  of  undecomposed  cement  together.  This  action 
causes  the  first  hardening,  or  initial  set,  as  it  is  called. 

After  the  initial  set  has  taken  place,  cements  slowly  increase 
in  strength.  The  final  hardening  is  due  to  the  slower  liberation  of 
lime  from  its  union  with  silica.  This  lime  also  crystallizes  out  and 
the  network  .of  crystals  so  formed  also  serves  as  a  binder  to  hold 
the  particles  together.  Hydraulic  cements  increase  in  strength 
with  time,  the  increase  extending  over  months  or  even  years.  This 
increase  is  due  to  the  slow  setting  of  the  coarser  particles. 

The  whole  subject  of  cement  setting  is,  however,  yet  in  a  con- 
troversial stage.  Dr.  Michaeles,  one  of  the  world's  leading  cement 
experts,  does  not  accept  the  crystallization  theory,  but  advocates 
what  is  termed  the  colloidal  theory  or  the  formation  of  mineral 
glue  in  the  process  of  hardening.  While  to  many  the  theory  of 
setting  appears  to  have  only  a  passing  value,  the  question  is  really 
of  great  importance  to  the  cement  manufacturer,  as  the  process, 
if  the  colloidal  theory  were  true,  could  be  much  simplified  and  the 
cost  of  manufacture  largely  reduced. 


HOW   CEMENTS   ARE   MADE 

The  difference  between  Portland,  Natural,  and  Slag  cements  is 
best  illustrated  by  comparing  their  methods  of  manufacture  as  de- 
scribed in  Table  I. 

Manufacture  of  Natural  Cement. — Natural  cement  is  produced 
by  the  burning  at  low  heat  and  subsequent  pulverization  of  natural 
limestone,  no  preliminary  mixing  or  grinding  being  required. 
This  natural  limestone  is  composed  of  an  argillaceous  carbonate  of 
lime  containing  varying  amounts  of  silica,  alumina,  and  iron 
oxide.  In  the  process,  the  carbon  dioxide  of  the  lime  stone  is 
almost  entirely  driven  off  and  the  silica,  alumina,  and  iron  oxide 


Handbook  for  Cement  and  Concrete  Users 

unite  with  the  lime  to  form  various  compounds.  When  this  burned 
mass  is  finely  ground  to  a  powder  and  mixed  with  water  it  hardens 
or  sets,  either  in  air  or  under  water. 

TABLE  I. — OUTLINE  OF  PROCESS  OF  MANUFACTURE  OF 
HYDRAULIC  CEMENTS 


Portland  Cement. 

Natural  Cement. 

Slag  Cement. 

i.  Grinding    of    raw    ma- 
terials. 
2.  Proportioning   and  mix- 
ing. 
3.  Burning. 
4.  Grinding  of  the  clinker. 

i.  Burning  of  the  natural 
rock  without  pulveriza- 
tion. 
2.  Grinding  of  the  clinker. 

i.  Cooling   of   hot  blast-fur- 
nace    slag      by     sudden 
immersion. 
2.  Grinding. 
3.  Mixing  with  slaked  lime. 

Quarrying  and  Crushing. — Since  the  rock  in  its  native  state 
contains  the  proper  proportion  of  the  ingredients  for  natural  cement, 
it  is  only  necessary  to  break  up  the  quarried  rock  into  convenient 
sizes  and  load  it  into  the  kiln.  In  order  to  insure  uniformity  of 
product,  it  is  common  practice  to  mix  rock  from  various  layers  in 
the  quarry,  so  that  the  deficiency  of  any  element  in  the  rock  from 
any  particular  stratum  may  be  corrected  by  a  corresponding  excess 
in  another  stratum.  The  rock  is  broken  up  in  ordinary  rock 
crushers  and  conveyed  either  by  belting  or  tramway  to  the  loading 
platform  at  the  top  of  the  kiln. 

Burning  and  Grinding. — The  kiln  used  in  the  manufacture  of 
natural  cement  is  usually  of  the  vertical  continuous  mixed-feed 
type  and  is  built  of  masonry  or  iron  lined  with  fire  brick.  The 
crushed  rock  and  the  fuel,  which  may  be  either  anthracite  or  bitu- 
minous coal  of  good  quality,  are  spread  in  the  kiln  in  alternate  layers 
and  the  mass  is  burned  at  an  average  temperature  of  about  1,600°  F., 
depending  upon  the  character  of  the  rock.  After  removal  from 
the  kiln  the  mass  is  sorted,  all  underburnt  and  overburnt  clinker 
being  rejected.  The  material  thus  rejected  usually  represents 
about  one-fourth  of  the  total.  The  calcined  rock  is  then  crushed 
in  a  pot  crusher  or  other  rotary  type,  and  screened.  The  finer 
materials  are  removed  to  the  bins,  while  the  coarse  particles  go 
through  a  further  process  of  grinding.  The  product  then  passes 
to  mixers,  by  means  of  which  a  uniformly  fine  product  is  assured. 

[10] 


Kinds  of  Cement  and  How  They  are  Made 

From  the  storage  bins  the  material  is  passed  through  chutes, 
and  then  to  the  bags  or  barrels  in  which  it  is  packed  for  final 
shipment. 

Manufacture  of  Portland  Cement.— Portland  Cement  is  pro- 
duced by  burning  to  incipient  fusion,  a  mixture  of  finely  ground 
argillaceous  and  calcareous  material,  and  the  subsequent  pulveriza- 
tion of  the  clinker  thus  obtained.  It  will  be  seen,  therefore,  that 
Portland  cement  differs  from  natural  cement  not  only  in  the  char- 
acter of  the  raw  material  employed,  but  also  in  the  quantity  of 
heat  required  in  its  manufacture. 

The  Raw  Materials. — The  materials  should  contain  approxi- 
mately the  following  quantities  of  the  essential  ingredients: 

Silica,  21-24  Per  cent;  alumina,  6-8  per  cent;  lime,  60-65  Per 
cent ;  with  small  amounts  of  iron  oxide,  magnesia,  -sulphuric  and 
carbonic  acids,  and  water.  These  materials  may  be  either  limestone 
and  clay,  marl  and  clay,  chalk  and  clay,  or  cement  rock  and  lime- 
stone, the  last  named  being  the  most  commonly  used. 

Processes. — The  method  of  mixing  of  the  raw  materials  in 
preparation  for  their  calcining  has  given  rise  to  two  processes,  known 
as  the  wet  process  and  dry  process  respectively. 

The  first  is  best  for  soft  or  wet  material  such  as  marl  and  clay, 
or  chalk  and  clay.  The  combined  mass  is  mixed  in  a  vat  or  wash 
mill  with  a  large  excess  of  water.  The  lumps  are  broken  up  with 
agitators  and  the  particles  are  so  finely  divided  as  to  be  held  in 
suspension  by  the  water.  The  stuff  is  then  drawn  off  into  a  settling 
basin  and  the  resultant  slurry  moulded  into  bricks  which  are  dried 
and  finally  calcined  in  stationary  kilns.  Owing  to  the  introduction 
of  rotary  kilns,  the  above  method  has  been,  to  a  great  extent,  super- 
seded by  a  semi-wet  process  which  is  substantially  as  follows: 

The  Semi-wet  Process. — The  marl  or  chalk  is  passed  through  a 
disintegrator  and  run  into  storage  basins,  while  the  clay  is  dried 
and  pulverized  and  mixed  with  the  proper  proportion  of  marl  in 
pans,  enough  water  being  added  to  give  the  mass  a  thick,  creamy 
consistency.  The  wet  mixture  is  then  ground  either  in  a  pug  mill 
or  edge  runner  and  run  into  slurry  tanks,  where  it  is  constantly 
stirred  by  means  of  pedals  or  compressed  air.  The  wet  slurry  is 
then  pumped  directly  into  rotary  kilns  and  burned  at  a  high  tem- 
perature. 


Handbook  for  Cement  and  Concrete  Users 

The  rotary  kiln  consists  of  a  brick-lined  steel  cylinder  varying 
from  50  to  200  ft.  in  length  and  from  5  to  12  ft.  in  diameter.  By 
means  of  appropriate  machinery  it  is  slowly  rotated  at  an  average 
speed  of  one  revolution  a  minute.  The  cylinder  is  usually  slightly 
inclined  to  the  horizontal  so  as  to  facilitate  the  movement  of  the 
material  to  the  point  of  discharge.  The  raw  material  is  introduced 
at  the  upper  end,  and  in  passing  through,  it  is  calcined  to  all  clinker, 
leaving  the  kiln  at  the  lower  end  as  hard,  glassy  lumps  ranging  from 
sand  to  pieces  one  inch  in  diameter.  The  fuel  used  is  generally 
finely  pulverized  coal,  which  is  blown  in  at  the  lower  end,  forming 
a  sheet  of  flame  extending  through  the  cylinder.  When  properly 
burned,  the  clinker  should  appear  in  the  form  of  an  irregular  ball 
of  greenish-black  color,  with  faint  metallic  lustre,  and  contain 
but  few  large  pieces. 

This  clinker,  red  hot  when  it  emerges  from  the  rotary,  drops 
into  a  conveyor  which  passes  under  water  jets,  cooling  the  clinker. 
When  thoroughly  cool,  the  clinker  passes  to  the  crusher  and  is  then 
ready  for  grinding.  The  material  undergoes  a  preliminary  grinding 
which  reduces  it  to  a  fineness  such  that  it  will  pass  through  a  No. 
20  or  30  sieve.  This  is  usually  done  by  the  ball-mill.  A  second 
grinding  renders  the  material  fine  enough  for  90  per  cent  to  pass 
through  a  No.  100  sieve,  this  finer  grinding  being  accomplished 
by  either  a  tube-mill,  Griffin  mill,  or  Lehigh  Fuller  mill. 

The  powder  is  then  conveyed  to  a  stock-house  and  seasoned 
for  a  time,  and  finally  passes  into  the  discharging  bins  whence  it  is 
weighed  out  into  bags  or  barrels  as  required  for  shipment. 

The  Dry  Process. — In  the  dry  process,  the  material  is  conveyed 
from  the  quarry  to  the  mill  and  is  crushed  to  pieces  varying  from 
dust  to  two  inches  in  diameter.  It  is  then  placed  into  storage  bins 
and  the  proper  proportions  decided  upon  by  chemical  analysis  of 
samples  taken  from  various  portions.  An  extremely  accurate 
mixture  is  obtained  by  using  an  automatic  weighing  machine  of 
the  tandem  type.  The  mixture  is  conveyed  to  a  dryer  which  usually 
consists  of  a  rotary  cylinder  worked  on  the  same  principle  as  the 
rotary  kiln,  heat  being  supplied  by  a  small  furnace.  The  tempera- 
ture is  sufficiently  high  to  cause  all  moisture  to  be  driven  off.  The 
material  is  then  ground  to  a  fineness  which  will  permit  it  to  pass 
through  a  screen  having  20  or  30  meshes  to  the  linear  inch;  then  is 

[12] 


Kinds  of  Cement  and  How  They  are  Made 

passed  on  to  the  fine  grinder  where  it  is  still  further  reduced  until 
from  80-90  per  cent  will  pass  a  screen  of  100  meshes  to  the  linear 
inch.  From  the  grinding,  machines,  the  finely  powdered  material 
is  conveyed  to  bins  from  which  it  is  automatically  fed  into  the  rotary 
kiln  for  calcining;  the  roasting  to  a  high  temperature  and  the 
subsequent  grinding  of  the  clinker  thus  formed  being  the  same  as 
in  the  semi-wet  process  already  described. 

White  Portland  Cements. — Within  recent  years  Portland  cements 
of  pure  white  color  have  come  into  the  market.  Such  cements  cost 
about  four  times  as  much  as  ordinary  Portland,  owing  to  the  ex- 
pense of  manufacture.  They  are,  however,  so  well  adapted  to  the 
attainment  of  architectual  and  artistic  effects  as  to  have  come  into 
extensive  use  for  the  following  purposes: 

1.  Building    ornamentation. — For    exteriors,     steps,     railings, 
columns,  doorways,  windows,  casings,  cornices,  and  panels. 

2.  Stucco. 

3.  Concrete  building  blocks. 

4.  Interior  Decoration.     Staircases,  wainscoting,  panels,  reliefs, 
floors. 

5.  Statuary. — An  improved  substitute  for  plaster  in  reproducing 
statuary  figures  and  groups  for  galleries  of  casts,  or  exterior  and 
interior  decoration. 

6.  Cemetery  Work. — For  monuments,  vaults,  columns,  urns,  etc. 

7.  Parks  and  Grounds. — For  fountains,  seats,  railings,  walks, 
bridges,  etc. 

8.  Tile,  Mosaic,  etc. — In  the  production  of  white  or  delicate 
tints  and  as  a  cement  in  place  of  Keene's  cement. 

9.  Colored   Concrete. — Permits  the  use  of  bright  or  delicate 
colors. 

10.  Painting  iron  work  or  concrete. 

11.  Stainless  mortar.     For  laying  up  Bedford  limestone,  sand- 
stone, or  marble. 

12.  Setting  and  pointing  between  blocks  or  slabs  of  white  marble, 
limestone,  or  brick. 

White  cement  is  mixed  with  white  sand,  crushed  white  quartz, 
ground  marble  (not  dust),  or  ground  white  limestone  to  produce 
white  concrete  or  white  artificial  stone.  For  the  development  of 
this  material,  credit  is  due  to  the  Sandusky  Portland  Cement  Co., 


Handbook  for  Cement  and  Concrete  Users 

and  to  the  Vulcanite  Cement  Co.,  who  are  the   pioneers  in  its 
production. 

Slag  or  Puzzuolan  Cement  is  produced  by  the  mixture  of 
granulated  blast-furnace  slag  and  slaked  lime,  and  the  reduction  of 
the  mass  to  a  fine  powder. 

Slag  of  proper  composition,  as  it  comes  from  the  blast  furnace, 
is  sprayed  with  a  stream  of  cold  water  under  pressure;  the  water 
granulates  the  slag  and  also  combines  with  the  elements  contained 
therein,  causing  evolution  of  sulphuretted  hydrogen  and  the  forma- 
tion of  lime.  The  slag  is  dried  and  then  ground,  first  in  a  Griffin 
mill  and  then  in  a  tube-mill.  The  lime  is  burned  from  very  fine 
limestone,  slaked,  screened,  and  dried,  and  is  then  incorporated 
with  the  slag.  The  resulting  material  is  fine  enough  to  permit  95 
per  cent  passing  through  a  No.  200  sieve.  Caustic  soda  is  added 
during  the  slaking  of  the  lime  in  order  to  produce  a  quick-setting 
cement. 

Plaster  Cements. — The  activity  of  the  cements  previously 
discussed  is  presumably  due  to  the  formation  of  crystals  containing 
lime  and  water.  There  is  another  class  of  cements,  the  activity  of 
which  is  due  to  the  crystallization  of  lime,  water,  and  sulphur  when 
chemically  combined.  This  substance  is  called  calcium  sulphate 
or  gypsum.  When  heated  and  reduced  to  powder,  it  is  known 
as  plaster,  plaster  of  Paris,  and  white  cement. 

Plaster  is  used  for  interior  walls,  ceilings,  and  decorations;  also 
for  reproducing  works  of  marble,  pottery,  and  bronze.  Plaster  is 
either  quick  or  slow  setting.  The  former,  when  mixed  with  its  own 
weight  of  water,  sets  in  five  minutes,  while  the  latter,  under  similar 
conditions,  takes  fifteen  minutes.  Plaster  heated  to  redness  and 
mixed  in  the  ordinary  manner,  will  no  longer  set ;  but  if,  instead  of 
applying  a  large  quantity  of  water,  the  smallest  possible  portion  is 
used,  it  will  set  in  ten  to  twelve  hours,  and  become  extremely  hard. 

The  compressive  strength  of  plaster  is  about  120  Ibs.  per  sq. 
in.  Plaster  adheres  to  itself  better  than  to  stone  or  brick.  The 
adhesion  to  iron  is  from  24  to  37  Ibs.  per  sq.  in. 

The  quality  of  plaster  may  be  tested  by  simply  squeezing  it  with 
the  hand.  If  it  coheres  slightly,  and  keeps  in  position  after  the 
hand  has  been  gently  opened,  it  is  good;  but  if  it  immediately  falls 
to  pieces,  it  has  been  injured  by  damp. 

[M] 


Kinds  of  Cement  and  How  They  are  Made 

Plaster  forms  the  basis  of  many  white  cements,  which  are  usually 
laid  in  two  coats;  the  first  of  cement  and  sand  is  about  1/2  to  3/4  in. 
thick.  The  second  coat  is  thinner  and  is  composed  of  neat  cement 
without  the  admixture  of  sand. 

Portland  cement  with  a  large  proportion  of  sand,  as  much  as 
90  per  cent  being  used,  is  useful  for  interior  work.  It  may  be  used 
as  a  backing  for  a  thin  floating  of  the  white  cements.  White  Port- 
land cements  are  also  used  as  a  final  coat  where  great  durability 
and  strength  are  required. 

Among  the  best  known  gypsum  cements  are  Parian  Cement, 
Keene's  Cement,  Martin's  Cement,  and  Adamant.  These  all  have 
plaster  of  Paris  for  their  base,  and  are  eminently  suited  to  interior 
work.  They  can  all  be  brought  to  a  good  surface,  and  can  be 
painted. 

Parian  Cement  is  hard  and  quick-setting  and  well  adapted  to 
withstand  rough  usage.  Keene's  Cement  is  harder  than  the  other 
kinds  made  from  plaster  of  Paris,  and  is  much  used  for  pilasters, 
columns,  etc. 

At  the  present  time  Portland  cement  almost  exclusively  is  used 
for  exterior  plastering  and  stucco  work. 

Choice  of  Cements. — The  selection  of  the  proper  grade  of 
cement  to  be  used  in  any  given  structure  is,  to  a  great  extent,  de- 
pendent upon  the  character  of  the  work.  That  cement  should  be 
selected  which  will  give  the  best  and  most  permanent  results  con- 
sistent with  the  limits  of  cost  of  the  work  in  question.  A  few 
general  rules  may  be  formulated  for  guidance  in  making  a 
selection. 

Portland  Cement  should  be  used  in  mortar  and  concrete  for 
structures  subjected  to  severe  or  frequently  recurring  stresses;  for 
all  work  laid  under  water  or  which  will  come  into  contact  with 
water  immediately  after  placing;  for  masonry  exposed  to  the  action 
of  the  elements.  The  White  Portland  is  eminently  fitted  for  high- 
class  ornamental  work  as  already  stated. 

Natural  Cement  may  be  used  in  concrete  for  dry  unexposed 
foundations  with  moderate  compression;  for  backing  or  filling  in 
massive  concrete  or  stone  masonry;  for  sewer  foundations  and  for 
sub-pavements  of  streets.  It  is  also  adapted  for  use  in  mortar,  for 
ordinary  brick  work,  and  for  ordinary  stone  masonry  where  the  chief 

hsl 


Handbook  for  Cement  and  Concrete  Users 

requisite  is  weight  or  mass.  It  should  never  be  used  in  work 
under  water,  in  marine  construction,  in  columns,  beams,  floors,  or 
other  members  subjected  to  severe  or  suddenly  applied  stresses. 
Puzzolan  or  Slag  Cement  is  limited  to  use  in  sea  water,  and  generally 
to  structures  constantly  exposed  to  moisture,  as  foundations  of 
buildings,  sewers  and  drains,  and  in  the  interior  of  heavy  masonry 
or  concrete.  It  is  unfit  for  use  when  subjected  to  mechanical  wear, 
abrasion,  or  blows,  and  should  never  be  used  where  it  may  be  ex- 
posed to  the  action  of  dry  air  for  long  periods.  Under  such  con- 
ditions it  will  turn  white  and  disintegrate,  owing  to  the  oxidation  of 
its  sulphides  at  the  surface. 

Hydraulic  Lime  is  extensively  employed  on  the  Continent, 
especially  in  France,  in  the  form  of  Beton-Coignet  (a  mixture  of 
hydraulic  lime  with  sand  and  cement). 

Common  Lime  mortar  is  usually  limited  to  brick  work  and  to 
chimney  construction  in  frame  houses. 

Lime  and  Cement  Mortar  is  suitable  for  ordinary  brickwork,  for 
light  rubble  foundations,  and  for  building  walls. 

Portland  cement,  owing  to  its  greatly  superior  strength  and 
reliability,  is  rapidly  displacing  all  other  kinds  of  cement,  and  it 
will  continue  to  do  so  even  more  rapidly  as  its  cost  is  lowered.  In 
the  following  chapters,  Portland  cement  is  always  referred  to  unless 
another  is  specifically  mentioned. 

How  Portland  Cement  Comes. — Portland  cement  comes  in  paper 
bags,  cloth  sacks,  or  wooden  barrels.  The  best  way  to  handle  it 
for  the  average  user  is  in  cloth  sacks.  The  manufacturers  charge 
more  for  this  kind  of  a  package,  but  allow  a  rebate  for  the  return 
of  the  empty  bags.  The  bags  must  be  kept  dry  and  untorn,  and 
shipped  back  by  freight,  in  exact  accord  with  the  requirements  of 
the  cement  company.  Paper  bags  tear  too  easily  and  cause  a  big 
percentage  of  loss,  especially  on  small  jobs  where  any  carrying  has 
to  be  done.  Barrels  are  too  bulky  to  handle  easily  and  are  too 
large  a  unit  for  measuring.  The  weight  of  the  shipping  units  of 
cement  varies  slightly,  but  in  general  a  paper  or  cloth  bag  contains 
95  Ibs.  of  cement,  and  four  such  bags  make  a  barrel  of  380  Ibs. 

How  to  Keep  Portland  Cement. — Cement  must  be  stored  in  a 
dry  place.  It  absorbs  moisture  from  the  atmosphere  with  great 
readiness,  and  soon  becomes  lumpy,  or  even  a  solid  mass,  when 

[16] 


Kinds  of  Cement  and  How  They  are  Made 

kept  in  a  damp  place.  Such  cement  is  useless  and  must  be  thrown 
away.  Lumpy  cement  should  not  be  broken  up  and  used  again, 
even  if  this  can  be  readily  done,  as  it  has  lost  by  far  the  greater  part 
of  its  adhesive  value.  In  storing  cement,  throw  wooden  blocks  on 
the  floor,  place  boards  over  them,  and  pile  the  cement  on  the  boards, 
covering  the  pile  with  canvas  or  pieces  of  roofing  paper. 


CHAPTER  III 

PROPERTIES,    TESTING,    AND    REQUIREMENTS    OF 
HYDRAULIC    CEMENTS 

Description   of  Tests. — How  the  Tests  are  Made. — Standard  Requirements  for 
Natural  and  Portland  Cements. 

Properties  of  Hydraulic  Cements. — The  properties  of  a  cement 
which  are  usually  examined  to  determine  its  constructive  value,  are : 
first,  color;  second,  weight;  third,  activity;  fourth,  soundness; 
fifth,  fineness;  and  sixth,  strength. 

Color  indicates  the  thoroughness  of  burning  and  the  presence 
of  impurities.  With  Portland  cement,  gray  or  greenish-gray  is  an 
indication  of  good  quality.  A  yellowish  shade  indicates  under- 
burned  material;  bluish-gray  an  excess  of  lime;  and  brown,  an 
ex'cess  of  clay.  For  decorative  purposes,  white  Portland  cements, 
having  all  of  the  properties  of  gray,  are  also  employed.  In  these 
the  color  does  not  indicate  any  inferiority  in  strength  or  setting 
power. 

Natural  cements  are  generally  brown,  in  light  or  darker  shades. 
A  light  color  generally  indicates  an  inferior  underburned  rock. 

For  any  particular  cement  the  weight  varies  with  the  degree  of 
heat  in  burning,  the  degree  of  fineness  in  grinding,  and  the  density 
of  packing.  Other  things  being  the  same,  the  harder-burned 
varieties  are  the  heavier.  The  finer  a  cement  is  ground,  the  more 
bulky  it  becomes,  and  consequently  the  less  it  weighs.  Hence  light 
weight  may  be  caused  either  by  laudable  fine  grinding  or  by  objec- 
tionable under-burning. 

A  barrel  of  Portland  cement,  containing  3.8  cu.  ft.,  should  weigh 
about  380  pounds  net;  natural  cements  weigh  from  250  to 300  pounds 
net  per  barrel. 

The  activity  of  a  cement  is  determined  by  its  rate  of  setting. 
For  most  purposes,  where  immediate  setting  is  not  required  to 
prevent  disturbance  of  the  mortar  before  hardening,  the  moderately 


Testing  and  Requirements  of  Hydraulic  Cements 


FIG.  i. — Showing  Normal  Ce- 
ment Pat  in  Good  Condition. 
(After  W.  Purves  Taylor.) 


slow-setting  cements  are  found  most  convenient,  as  they  need  not 
be  handled  so  quickly  and  may  be  mixed  in  somewhat  larger  quanti- 
ties. 

Soundness  is  the  most  important  quality  of  a  cement,  as  it 
means  the  power  of  the  cement  to  resist  the  disintegrating  influences 
of  the  atmosphere  or  water  in  which 
it  may  be  placed.  Soundness  refers 
to  the  property  of  not  expanding, 
contracting,  or  cracking  during  the 
time  of  setting.  These  effects  may 
be  due  to  free  lime,  free  magnesia, 
or  to  unknown  causes. 

The  question  of  fineness  is  wholly 
a  matter  of  economy.  Cement,  until 
ground,  is  a  mass  of  partially  vitrified 
clinker,  which  is  not  affected  by 
water,  and  which  has  no  setting 
power.  It  is  only  after  it  is  ground 
that  the  addition  of  water  induces  crystallization.  The  coarse  parts 
of  the  cement  may  be  considered  as  practically  inert  material 
which  sets  only  after  the  lapse  of  months  or  years  if  at  all.  It  is 

the  impalpable  powder  whicH  gives 
the  cement  its  value,  and  if  this  be 
omitted,  the  cement  is  worthless. 

It  is  possible  to  reduce  a  cement 
to  an  impalpable  powder.  Fine 
grinding  is,  however,  expensive.  The 
proper  degree  of  fineness  is  reached 
when  it  becomes  cheaper  to  use  more 
cement  in  proportion  to  the  aggre- 
gate, than  to  pay  the  extra  cost  of 
additional  grinding. 

The  strength  of  cement  is  usually 
determined  by  submitting  a  specimen 
of  known  cross-section  to  a  tensile  strain.  The  reason  for  adopt- 
ing tensile  tests  is  that  comparatively  light  strains  produce  rupture. 
This  will  be  referred  to  later. 


FIG.  2. — Pat  Showing  Shrinkage 
Cracks  Due  to  Overwet  Mixture 
or  Too  Rapid  Drying. 


Handbook  for  Cement  and  Concrete  Users 


HOW  CEMENT  IS  TESTED 

Having  outlined  the  nature  and  properties  of  hydraulic  cements, 
we  now  propose  to  take  up  the  methods  that  may  be  employed  by 
the  cement  user  to  determine  whether  the  material  he  purchases  is 
up  to  the  standard  and  fit  for  use. 

The  testing  of  cement  for  use  on  extensive  work  has  become 
an  art  in  itself  and  only  men  experienced  in  the  work  can  obtain 
results  that  are  uniform  and  reliable.  It  is  therefore  not  intended 
to  go  into  details  of  apparatus  and  methods  employed  by  the  skilled 


FlG.  3. — Pats  Showing  Cracks  Due  to  Incipient  Disintegration  and  which  Warrant 

Rejection. 

tester  which  are  of  little  use  to  the  practical  cement  user,  but  an 
idea  of  what  is  done  is  of  general  interest. 

Physical  Tests  for  Cement. — On  all  large  works,  an  inspector 
is  kept  at  the  mills  to  watch  the  process  of  manufacture,  and  special 
laboratories  are  provided  for  making  both  chemical  and  physical 
examinations.  As  already  stated,  the  physical  examination  is 
employed  to  determine  whether  the  cement  possesses  the  necessary 
requirements  to  make  it  fit  for  use.  Thus  a  good  cement: 

First. — Should  be  sufficiently  well  ground.  This  is  referred  to 
as  a  test  for  fineness  and  is  made  by  passing  the  cement  through 
sieves  of  varying  meshes.  In  a  good  Portland  98  per  cent  should 
pass  through  a  No.  100  sieve,  having  10,000  holes  to  the  square 
inch.  The  finer  the  cement  is  ground  the  greater  will  be  its  hydrau- 
licity,  and  the  greater  the  proportions  of  sand  that  can  be  used  with  it. 

[20] 


Testing  and  Requirements  of  Hydraulic  Cements 

Second. — Setting. — Cement  which  sets  much  too  rapidly  or  does 
not  set  rapidly  enough  may  not  be  fit  for  use.  This  may  be  due  to 
the  presence  of  too  much  gypsum  or  the  cement  may  not  be  suffi- 
ciently hydraulic.  Furthermore,  a  quick-setting  cement  may  be 
desired  for  certain  work  and  slow-setting  for  other.  To  determine 
the  setting  properties  it  is  customary  to  prepare  pats  about  3  inches 
in  diameter  and  1/2  inch  thick  in  the  middle  and  with  thin  edges 
on  glass  plates,  and  allow  them  to  set.  When  the  pat  just  resists 
the  pressure  of  a  needle  -^  inch  in  diameter  weighted  with  1/4  pound 
it  is  said  to  have  had  its  initial  set.  This  is  usually  within  1/2 


FIG.  4. — Pats  Showing  Cracks  of  Complete  Disintegration  which  Begin  by  the 
Radial  Cracks  Shown  in  Fig.  3. 

hour  to  i  hour  and  the  process  of  manufacture  may  be  regulated  to 
obtain  the  required  time  of  initial  set  for  the  work  in  hand.  Cement 
for  use  under  water  or  in  freezing  weather  should  be  quick-setting. 
When  cement  has  once  received  its  initial  set  after  being  mixed  for 
use,  it  should  not  be  remixed  with  water  or  retempered  for  use,  as 
the  setting  properties  and  strength  have  been  greatly  disturbed, 
although  when  hardened  cement  is  reground  it  still  possesses  con- 
siderable setting  power.  The  final  set  of  cement  occurs  when  it 
can  just  resist  the  pressure  of  a  needle  1/24  inch  in  diameter  weighted 
with  i  pound.  The  time  of  final  setting  varies  from  3  or  4  to  10 
hours;  the  quick-setting  cements  are  usually  stronger  at  first,  but 
the  slower-setting  cements  acquire  greater  strength  than  the  others 
in  course  of  time. 

An  excellent  method  of  testing  for  setting  is  to  prepare  a  ball  of 

[21] 


Handbook  for  Cement  and  Concrete  Users 

cement  and  allow  it  to  set  protected  from  sun  and  wind.  At  the 
end  of  20  minutes  it  should  be  soft  and  pliable,  damp  and  not  warm 
on  exterior  surface.  At  10  hours  it  should  be  dry,  firm,  and  hard 
enough  to  resist  pressure  of  thumb  nail.  If  it  hardens  or  heats  in 
less  than  20  minutes  the  cement  should  be  rejected,  as  it  will  set 
before  the  concrete  is  put  into  place.  A  cement  which  will  not  set 
in  10  hours  will  cause  difficulty  in  placing  the  concrete  and  a  satis- 
factory cement  should  set  within  these  limits. 

The  heating  referred  to  is  due  to  free  lime  and,  if  in  excess,  the 
cement  should  not  be  used.  Storage  will  convert  the  free  lime  into 
a  hydrated  condition  in  time,  and  it  can  then  possibly  be  used. 

Both  the  pat  and  ball  tests  are  also  serviceable  in  determining 
the  presence  of  free  lime.  This  free  lime  causes  heating  when 
mixed  with  water  and  also  expands  in  volume,  causing  cracking  of 
the  pat  or  ball.  When  used  in  the  work,  over-limed  cement  may 
cause  disintegration. 

The  presence  of  free  lime  can  better  be  determined  by  subjecting 
the  pat  or  ball  to  a  hot  steam  bath  for  an  hour  or  two,  after  which 
it  should  still  remain  sound  and  free  from  cracks.  The  presence 
of  lime  may  also  be  determined  by  treating  the  cement  with  muriatic 
acid  3  parts,  water  i  part,  cement  1/3  part.  A  good  cement  will 
effervesce  about  two  seconds.  If  it  effervesces  continually  it  con- 
tains too  much  limestone  or  natural  cement  and  should  not  be  used. 

Cement  in  the  laboratory  is  also  subjected  to  what  is  known  as 
the  " Specific  Gravity"  test  made  by  special  apparatus  and  not 
available  to  the  cement  user  on  the  work.  The  usual  specific 
gravity  of  a  good  Portland  is  about  3.2.  A  much  greater  value 
shows  everburning  and  a  lower  quantity  indicates  underburning  or 
adulteration. 

The  test  most  frequently  quoted  is  that  for  tensile  strength  which, 
like  the  previous  one,  cannot  usually  be  made  by  the  cement  user, 
as  time  and  apparatus  are  required,  while  uniform  and  reliable 
results  depend  upon  the  skill  and  experience  of  the  tester.  The 
tests  are  made  by  moulding  briquettes  into  shape  like  a  figure  8 
having  a  cross-section  in  the  centre  of  exactly  i  square  inch.  These 
briquettes  are  allowed  to  set  either  i,  7,  or  28  days  and  sometimes 
for  even  longer  periods  running  into  many  years.  They  are  then 
broken  in  testing  machines.  The  briquettes  are  made  both  of  pure 


Testing  and  Requirements  of  Hydraulic  Cements 

cement  and  of  cement  mortar  mixed  with  varying  proportions  of 
sand.  These  tests  are  of  value  because  long  years  of  experience 
have  fixed  certain  values  which  a  good  cement  should  obtain  and 
although  pure  cement  is  little  used  in  practice,  a  standard  is  thus 
fixed  which  serves  as  a  basis  of  comparison  for  different  cements. 

Tests  are  also  made  on  large  works  by  moulding  beams,  slabs, 
blocks,  and  columns  of  various  mixtures  of  concrete,  which  are 
later  subjected  to  special  machines,  and  broken  by  bending,  shear- 
ing, or  compression,  and  the  actual  strength  determined. 

It  is  proper  to  say  here  that  to  the  credit  of  American  cement 
manufacturers,  the  consumer  need  have  but  little  fear  of  the  quality 
of  the  cement  he  uses.  The  great  bulk  of  cement  of  any  of  the 
standard  brands  will  pass  the  ordinary  requirements.  Moreover 
the  cement  work  in  most  structures  is  never  subjected  to  anything 
like  the  stresses  that  the  strength  tests  show  it  is  able  to  withstand. 
It  is  only  in  work  where  very  high  unit  stresses  are  employed,  such 
as  in  reinforced  concrete  structures  that  the  actual  strength  of  the 
material  is  really -approached.  It  is  due  largely  to  the  uniformly 
good  quality  of  cement  turned  out  that  the  greatest  confidence  has 
been  established  in  the  mind  of  the  consumer  as  to  its  use  without 
testing,  and  it  is  due  largely  to  such  confidence  that  the  cement 
industry  owes  its  rapid  growth,  for  without  it  the  present  phenomenal 
expansion  would  have  been  impossible. 

The  ordinary  cement  user  should  be  particularly  careful  about 
two  things  in  a  newly  received  shipment  of  cement.  In  times  of 
great  building  activity  when  the  cement  mills  are  run  up  to  fall 
capacity,  there  is  danger  of  having  the  cement  too  fresh,  and  in 
such  cases  he  should  order  it  a  month  or  so  ahead  of  time  so  as  to 
improve  it  by  storage  as  already  referred  to.  The  second  thing  is 
to  see  that  the  cement  has  not  been  injured  in  transit  or  storage, 
for  if  dampness  has  reached  the  cement  it  will  be  lumpy  and  partially 
set  and  its  usefulness  be  largely  destroyed. 

REQUIREMENTS  FOR  CEMENTS 

The  following  are  the  requirements  for  natural  and  Portland 
cement  prepared  by  the  National  Association  of  Cement  Users, 
after  an  exhaustive  study  of  the  subject. 


Handbook  for  Cement  and  Concrete  Users 


STANDARD  REQUIREMENTS  FOR  NATURAL  CEMENT 

Definition.  — This  term  shall  be  applied  -to  the  finely  pulverized 
product  resulting  from  the  calcination  of  an  argillaceous  limestone 
at  a  temperature  only  sufficient  to  drive  off  the  carbonic  acid  gas. 

Fineness. — It  shall  leave  by  weight  a  residue  of  not  more  than 
10  per  cent  on  the  No.  100,  and  30  per  cent  on  the  No.  200  sieve. 

Time  of  Setting. — It  shall  not  develop  initial  set  in  less  than  ten 
minutes,  and  shall  not  hard  set  in  less  than  thirty  minutes,  or  in 
more  than  three  hours. 

Tensile  Strength. — The  minimum  requirements  for  tensile 
strength  for  briquettes  one  inch  square  in  cross-section  shall  be 
within  the  following  limits,  and  shall  show  no  retrogression  in 
strength  within  the  periods  specified: 

NEAT  CEMENT. 

Age.  Strength,    Lbs. 

24  hours  in  moist  air 50-100 

7  days  (i  day  in  moist  air,  6  days  in  water) 100-200 

28  days  (i  day  in  moist  air,  27  days  in  water) 200-300 

ONE  PART  CEMENT,  THREE  PARTS  STANDARD  SAND. 

7  days  (i  day  in  moist  air,  6  days  in  water) 25-  75 

28  days  (i  day  in  moist  air,  27  days  in  water)   75-150 

Constancy  of  Volume. — Pats  of  neat  cement  about  three  inches 
in  diameter,  one-half  inch  thick  at  centre,  tapering  to  a  thin  edge, 
shall  be  kept  in  moist  air  for  a  period  of  twenty-four  hours. 

(a)  A  pat  is  then  kept  in  air  at  normal  temperature. 

(b)  Another  is  kept  in  water  maintained  as  near   70°  F.  as 
practicable. 

These  pats  are  observed  at  intervals  for  at  least  28  days,  and, 
to  satisfactorily  pass  the  tests,  should  remain  firm  and  hard  and  show 
no  signs  of  distortion,  checking,  cracking,  or  disintegrating. 


STANDARD  REQUIREMENTS  FOR  PORTLAND  CEMENT 

Definition. — This    term    is    applied    to    the    finely    pulverized 
product  resulting  from  the  calcination  to  incipient  fusion  of  an 

[24] 


Testing  and  Requirements  of  Hydraulic  Cements 

intimate  mixture  of  properly  proportioned  argillaceous  and  calcare- 
ous materials,  and  to  which  no  addition  greater  than  3  per  cent 
has  been  made  subsequent  to  calcination. 

Specific  Gravity. — The  specific  gravity  of  the  cement  ignited  at 
a  low  red  heat  shall  not  be  less  than  3.10;  and  the  cement  shall  not 
show  a  loss  on  ignition  of  more  than  4  per  cent. 

Fineness. — It  shall  leave  by  weight  a  residue  of  not  more  than 
8  per  cent  on  the  No.  100,  and  not  more  than  25  per  cent  on  the 
No.  200  sieve. 

Time  of  Setting. — It  shall  not  develop  initial  set  in  less  than 
thirty  minutes;  and  must  develop  hard  set  in  not  less  than  one  hour, 
nor  more  than  ten  hours. 

Tensile  Strength. — The  minimum  requirements  for  tensile 
strength  for  briquettes  one  inch  square  in  section  shall  be  within 
the  following  limits,  and  shall  show  no  retrogression  in  strength 
within  the  periods  specified: 

NEAT  CEMENT. 

Age.  Strength,  Lbs. 

24  hours  in  moist  air 150-200 

7  days  (i  day  in  moist  air,  6  days  in  water) 450-550 

28  days  (i  day  in  moist  air,  27  days  in  water) 550-650 

ONE  PART  CEMENT,  THREE  PARTS  SAND. 

7  days  (i  day  in  moist  air,  6  days  in  water)  150-200 

28  days  (i  day  in  moist  air,  27  days  in  water)   200-300 

Constancy  of  Volume. — Pats  of  neat  cement  about  three  inches 
in  diameter,  one-half  inch  thick  at  the  centre,  and  tapering  to  a  thin 
edge,  shall  be  kept  in  moist  air  for  a  period  of  twenty-four  hours. 

(a)  A  pat  is  then  kept  in  air  at  normal  temperature  and  observed 
at  intervals  for  at  least  28  days. 

(b)  Another  is  kept  in  water   maintained   as   near   70°  F.    as 
practicable  and  observed  at  intervals  of  at  least  28  days. 

(c)  A  third  pat  is  exposed  in  any  convenient  way  in  an  atmos- 
phere of  steam,  above  boiling  water,  in  a  loosely  closed  vessel,  for 
five  hours.     These  pats,   to  satisfactorily  pass  the   requirements, 
shall  remain  firm  and  hard  and  show  no  sign  of  checking,  crack- 
ing, and  disintegrating. 


CHAPTER  IV 

CONCRETE  AND  ITS  PROPERTIES 

What  Concrete  Is. — Kinds  of  Concrete. — Function  and  Effect  of  the  Cement, 
Aggregates,  Water,  Chemicals,  Weather  Conditions,  Gases,  Sewage,  etc. — Laws 
of  Strength  and  Permeability. 

CONCRETE  is  an  artificial  rock,  made  by  uniting  sand,  broken 
stone,  gravel,  etc.,  by  means  of  lime  or  cement.  Its  principal 
ingredients  are  as  follows: 

1.  The  matrix  or  mortar;  consisting  of  cement  and  sand  mixed 
with  water. 

2.  The  coarse  aggregate;  broken  stone,  gravel,  etc. 

Concrete  made  with  good  Portland  cement,  in  proper  propor- 
tions, becomes  so  hard  and  strong  that  when  pieces  are  broken,  the 
line  of  fracture  will  often  be  found  to  pass  through  the  particles  of 
stone,  showing  that  the  adhesion  of  the  cement  to  the  stone  is 
greater  than  the  strength  of  the  stone  itself. 

Kinds  of  Concrete. — While  concrete  is  generally  composed  of 
cement,  sand,  and  broken  stone  or  gravel,  the  following  special 
combinations  are  also  used : 

1.  Rubble  concrete,  also  called  Cyclopean  masonry. 

2.  Cinder  concrete. 

3.  Asphalt  concrete. 

4.  Reinforced  concrete. 

In  constructing  massive  walls  and  dams,  a  reduction  in  cost  may 
often  be  obtained  by  introducing  large  stones  into  the  concrete. 
Concrete  of  this  character  is  called  Rubble  Concrete  or  Cyclopean 
Masonry.  The  percentage  of  rubble  stones  employed  varies  from 
a  few  per  cent  to  over  half  the  volume.  The  saving  effected  comes 
partly  from  the  reduction  in  the  cement  required  per  cubic  yard  of 
concrete  and  partly  from  the  saving  in  crushing. 

Cinder  concrete  is  used  where  great  strength  is  not  required. 
Its  most  valuable  properties  are  its  light  weight  and  the  resistance 
which  it  offers  to  heat.  It  is  therefore  used  for  fireproofing  and  light 
floor  construction. 

[26] 


Concrete  and  Its  Properties 

Cinder  concrete  is  weak  and  porous.  It  is  not  adapted  to 
reinforced  work  because  it  is  so  porous  that  it  does  not  protect  the 
steel  from  corrosion.  When  used,  great  care  must  be  taken  in  the 
mixing  and  proportioning  of  the  ingredients.  A  rich  mixture  of 
cement  should  always  be  required. 

Asphalt  or  tar  concrete,  in  which  broken  stone  or  cinders  are 
mixed  with  asphaltum  or  tar  instead  of  cement  paste,  is  used  for 


CEMENT 


SAND 


STONE 


CONCRETE 


FIG.  5. — Relative  Proportions  of  Ingredients  for  a  1:2:4  Concrete  Mixture. 
Note  that  the  volume  of  Concrete  is  but  slightly  larger  than  the  volume  of  Stone, 
the  Cement  and  Sand  filling  the  voids. 

waterproofing  and  for  lining  reservoirs  and  constructing  mill  floors. 
Such  mixtures  differ  in  degree  only  from  the  asphaltic  cements 
that  are  employed  for  street  pavings.  Their  most  valuable  proper- 
ties are,  imperviousness  to  water  and  elasticity. 

Reinforced  concrete,  in  which  concrete  is  combined  with  steel  or 
iron  to  develop  the  elastic  properties  of  the  latter  and  at  the  same 
time  utilizing  the  great  compressive  resistance  of  the  former.  This 
is  fully  discussed  in  Chapter  XVI  and  those  following. 


FUNCTION  AND  EFFECT  OF  VARIOUS  AGENCIES  ON 
CONCRETE  WORK 

In  considering  the  properties  of  concrete  and  how  it  is  af- 
fected by  various  agencies,  it  is  well  to  keep  clearly  in  mind  what 
concrete  actually  is  and  what  its  constituent  parts  actually  are. 
The  sand  and  gravel  is  natural  rock  disintegrated  by  natural  forces. 
The  broken  stone  is  natural  rock  disintegrated  by  artificial  forces. 
The  water  is  just  ordinary  H2O  which  is  clean  and  free  from  acids 
or  alkalis.  The  cement  has  already  been  described. 

An  ideal  concrete  is  a  mixture  with  a  minimum  percentage  of 
voids.  This  result  is  obtained  by  grading  the  aggregate  and 


Handbook  for  Cement  and  Concrete  Users 

mixing  in  such  proportions  that  the  voids  in  the  coarsest  aggregate 
are  filled  by  a  finer  aggregate,  the  voids  in  which  are,  in  turn,  filled 
by  a  still  finer  aggregate,  the  cement  itself  being  so  finely  ground 
that  its  granules  will  completely  coat  those  of  the  finest  aggregate. 
When  this  condition  obtains,  the  set  will  produce  a  mass  of  ever- 
lasting stone. 

Many  experiments  have  been  made  to  show  the  effect  on  the 
strength  of  concrete  of  the  admixture  of  various  materials  such  as 
loam,  clay,  lime,  plaster,  peat,  puzzolan,  cement,  salt,  sawdust, 
soda,  sugar,  alcohol,  glycerine,  and  tallow.  While  some  valuable 
practical  use  is  made  of  such  admixtures,  the  results  are  largely  of 
theoretical  interest. 

Cement  is  the  vital  element  of  concrete.  Upon  its  quality  the 
strength  and  durability  of  the  concrete  largely  depends.  It  binds 
the  particles  of  aggregate  together,  helps  to  fill  the  voids,  gives 
density,  and  according  to  its  strength  or  weakness,  imparts  like 
qualities  to  the  concrete. 

Influence  of  the  Aggregates. — Crushed  quartz,  crushed  brick, 
crushed  terra  cotta,  crusher  dust  and  sand  have  all  been  used  as 
the  finer  aggregate  in  concrete,  the  use  of  sand  being  most  prevalent. 

While  the  properties  and  selection  of  sand  are  fully  discussed 
in  the  next  chapter  we  may  state  here  that  sand  should  be  coarse 
rather  than  fine,  and  of  graded  rather  than  of  uniform  size  in  order 
that  a  dense  concrete  shall  result.  It  is  customary  to  specify  that 
sand  shall  be  free  from  clay  or  loam.  In  a  rich  mortar,  the  surplus 
cement  furnishes  enough  fine  material  for  the  density  required. 
The  addition  of  clay  tends  to  increase  the  density  and  the 
strength,  particularly  in  lean  mixtures.  Five  per  cent  may  be 
allowed.  A  similar  effect  is  produced  by  the  addition  of  a  small 
quantity; of  hydrated  lime  or  waterproofing  compound  to  cement 
mortar,  the  density  and  water-tightness  being  increased. 

For  the  coarse  aggregate  a  variety  of  materials  are  in  common 
use.  Crushed  stone,  such  as  trap  rock,  granite,  limestone,  conglom- 
erate, sandstone,  and  slate,  also  gravel  and  cinders,  give  satisfac- 
tion. Trap  and  granite  give  a  hard  wearing  surface  to  the  concrete, 
and  are  useful  as  aggregates  in  all  classes  of  concrete  work.  Gravel 
and  conglomerate  are  almost  equally  valuable.  These  are  fully 
discussed  in  Chapter  V. 

[28] 


Concrete  and  Its  Properties 

Function  and  Influence  of  the  Water. — The  function  of  water 
in  mixing  concrete  is  to  develop  the  chemical  activity  of  the  cement. 
The  proportion  of  water  used  has  an  important  bearing  on  the 
results  attained.  Both  the  time  of  setting  and  the  strength  are 
affected.  A  very  fine  cement  will  require  a  larger  proportion  of 
water  than  a  coarser  cement,  in  order  to  give  the  same  degree  of 
consistency.  Too  little  water  will  produce  a  weak  mortar,  as  part 
of  the  cement  will  be  unaffected.  Too  much  water  will  cause  a 
slight  decomposition  of  the  cement,  some  of  which  will  pass  off  in 
solution,  and  thus  weaken  the  mortar.  The  phenomenon  of 
"Laitance"  is  the  result  of  an  excess  of  water.  This  is  particularly 
noticeable  when  concrete  is  deposited  under  water,  a  white  scum 
appearing  at  the  surface. 

"The  effect  of  different  proportions  of  water  upon  the  ultimate 
strength  depends  chiefly  upon  the  density  of  the  resulting  mortar; 
the  consistency  which  produces  with  a  given  weight  of  the  same 
materials,  the  smallest  volume,  after  setting,  of  Portland  cement 
paste  or  mortar,  gives  the  highest  strength.  Dry-mixed  mortars 
usually  test  higher  than  wet  after  short  periods,  as  they  set  and 
harden  more  rapidly,  but  more  uniform  results  -in  practice  can  be 
attained  with  plastic  mixtures." 

Experiment  has  shown  that  coarse,  medium,  and  fine  sand 
require  respectively  3  per  cent,  9  per  cent,  and  23  per  cent  by 
weight  of  water.  "In  many  classes  of  structures  where  there  is 
an  excess  of  strength,  cheapness  in  placing,  the  appearance  of  the 
surface,  or  the  proper  inbedding  of  reinforcing  metal  may  be  of 
primary  importance.  In  such  cases  the  quantity  of  water  must  be 
suited  to  the  attendant  conditions." 

Dry  concrete  may  be  employed  in  dry  locations  for  mass  founda- 
tions, which  must  withstand  severe  compression  strain  within  one 
month  after  placing,  provided  it  is  carefully  spread  in  layers  not 
over  6  inches  thick  and  thoroughly  rammed. 

Medium  wet  concrete  is  adapted  for  ordinary  mass  concrete, 
such  as  foundations,  heavy  walls,  large  arches,  piers,  and  abutments. 

Very  wet  concrete  is  suitable  for  rubble  concrete  and  for  rein-  - 
forced  concrete,  such  as  thin  walls,  columns,  floors,  conduits,  and 
tanks.     Grout  or  liquid  concrete  is  discussed  in  Chapter  XXXI. 

Effect  of  Coloring  Matter. — Various  coloring  matters,  such  as 


Handbook  for  Cement  and  Concrete  Users 

carbon  black,  iron  oxide,  ochre,  ultramarine,  marble  dust,  and 
white  sand  are  used  in  concrete  for  aesthetic  effects.  As  a  rule, 
the  color  is  not  permanent.  The  effect  of  these  ingredients  upon 
the  strength  of  the  concrete  varies  with  the  material  used.  They 
may  be  mixed  dry  with  the  cement  and  then  submitted  to  the  usual 
tests.  If  of  mineral  origin,  their  addition  in  small  quantities  will 
not  affect  the  concrete.  They  rather  increase  its  density.  If  of 
vegetable  origin,  they  are  apt  to  impair  the  strength.  In  general, 
it  is  safe  to  specify  that  coloring  matter  shall  be  made  from  metallic 
oxides  free  from  sulphur.  Five  per  cent  of  materials  of  a  mineral 
character  may  be  allowed. 

Effect  of  Oils. — Mineral  oil  when  mixed  with  concrete  forms 
an  emulsion  with  the  alkali  and  water,  resulting  in  a  less  brittle 
mortar  and  one  much  more  free  from  expansion  and  contraction 
cracks.  The  oil  also  has  the  effect  of  delaying  the  initial  and  final 
set  somewhat  and  of  decreasing  the  strength  to  a  small  extent. 
The  use  of  animal  or  vegetable  oils  is  not  recommended,  because 
the  result  is  the  formation  of  acids,  which  are  apt  to  cause  disinte- 
gration of  the  concrete.  Oil  emulsions  have  formed  the  basis  of 
many  waterproofing  compounds  and  when  mineral  oils  are  used 
they  add  to  the  density  and  quality  of  the  work. 

Fire-resisting  Properties. — Concrete  possesses  great  fire-resisting 
properties.  In  a  severe  fire  when  subjected  to  a  heat  as  great  as 
2,000°  F.,  concrete  is  injured  to  a  depth  of  perhaps  one  inch,  its 
body  being  unaffected.  Two  inches  of  good  concrete  is  ample 
protection  against  fire  for  I-beams  or  steel  rod  reinforcements. 
"  When  brick  and  terra-cotta  are  heated,  no  chemical  action  occurs, 
but  when  concrete  is  heated  up  to  1,000°  F.,  its  surface  becomes 
decomposed,  dehydration  occurs,  and  water  is  driven  off.  This 
process  takes  a  relatively  great  amount  of  heat.  It  would  take 
about  as  much  heat  to  drive  the  water  out  of  this  outer  quarter 
inch  of  the  concrete  partition,  as  it  would  to  raise  that  quarter  inch 
to  1,000°  F.  Now  a  second  action  begins.  After  dehydration, 
the  concrete  is  much  improved  as  a  non-conductor,  and  yet  through 
this  layer  of  non-conducting  material  must  pass  all  the  heat  to 
dehydrate  and  raise  the  temperature  of  the  layers  below,  a  process 
which  cannot  proceed  with  great  speed." 

Effect  of  Weather  Conditions. — Heat  hastens  and  cold  retards 

[30] 


Concrete  and  Its  Properties 

the  set  of  cement.  Therefore,  a  quick-setting  cement  should  be 
employed  in  winter  and  a  slow-setting  cement  in  summer.  The 
sun's  heat  will  cause  too  rapid  evaporation  which  must  be  guarded 
against  as  it  weakens  the  concrete. 

Severe  cold  or  frost  rarely  causes  greater  damage  than  surface 
disintegration.  The  setting  process  discontinues  at  freezing,  but 
starts  again  when  the  temperature  rises  above  the  freezing-point. 
This  does  not  injure  the  concrete,  but  merely  prolongs  the  attain- 
ment of  its  ultimate  strength.  Alternate  freezing  and  thawing, 
however,  absolutely  ruin  concrete. 

Salt  water,  up  to  a  lo-per-cent  solution  for  concrete,  delays  the 
set,  but  does  not  weaken  the  concrete.  If  a  stronger  solution  is 
used  the  salt  is  apt  to  work  to  the  surface  and  cause  unsightly  stains. 

Effect  of  Sea  Water. — Sea  water  is  objectionable  for  gauging 
mortars  and  concrete  not  because  of  its  salt,  but  because  the  mag- 
nesium sulphate  in  water  reacts  chemically  with  the  lime  in  the 
cement,  forming  various  compounds  and  resulting  in  the  gradual 
rotting  of  the  cement  and  the  eventual  failure  of  the  concrete.  A 
dense  concrete  protected  from  the  action  of  the  sea  water  until  the 
cement  has  thoroughly  set  is  in  little  danger  of  injury. 

Some  concrete  masonry  has  remained  intact  for  a  very  long 
time  in  sea  water;  on  the  other  hand,  structures  subject  to  similar 
conditions  have  been  ruined  in  a  few  years.  Experience  has  shown 
that  the  cement  for  use  in  marine  construction  should  be  as  low  as 
possible  in  aluminum  and  lime.  Puzzolan  material  is  a  valuable 
addition  to  the  cement,  as  it  unites  with  the  lime  to  form  insoluble 
compounds  upon  which  the  sulphuric  acid  of  the  sea  water  finds 
difficulty  in  making  an  impression.  As  little  gypsum  as  possible 
should  be  added  for  regulating  the  time  of  setting.  Sand  containing 
a  large  proportion  of  fine  grains  is  unsuitable  altogether,  as  the  per 
cent  of  voids  is  dangerously  large.  The  concrete  should  be  pro- 
portioned to  secure  as  great  a  density  and  impermeability  as  possible, 
thereby  excluding  chemical  action  from  the  interior  of  the  mass. 

Effect  of  Gases,  Acids,  Sewage,  etc.— Gases  have  little  or  no  effect 
upon  the  durability  of"  the  concrete,  unless  the  peculiar  character 
of  the  aggregate  happens  to  have  a  chemical  affinity  for  the  par- 
ticular gas  to  which  it  is  subjected.  Certain  surface  effects  have 
been  noted  in  concrete  arches  and  tunnel  linings,  which  have  been 


Handbook  for  Cement  and  Concrete  Users 

exposed  to  the  hot  gases  from  passing  locomotives,  but  in  no  case 
has  the  integrity  of  the  concrete  mass  been  threatened.  The  great 
objection  to  gases  is  the  resulting  disfigurement  of  the  surface. 

Strong  acids  will  affect  a  concrete  surface,  but  with  a  silicious 
or  igneous  aggregate,  the  effect  will  be  a  slight  surface  etching. 
Marked  disintegration  has  been  noted  in  concrete  exposed  to  certain 
kinds  of  sewage.  The  conditions  favoring  disintegration  are  altern- 
ate immersion  of  the  concrete  surface  in  the  sewage  and  exposure 
to  the  air.  Sewage  contains  large  amounts  of  sulphuretted  hydrogen 
in  solution.  When  the  level  of  the  liquid  falls,  it  leaves  the  concrete 
wet  with  this  solution,  which  may  cause  oxidation  and  disintegration. 

Alternate  rise  and  fall  of  the  liquid  level  erodes  the  decomposed 
cement  and  exposes  new  concrete  to  the  attack  of  the  acid.  The 
effect  being  cumulative,  the  integrity  of  the  concrete  mass  is  eventu- 
ally threatened.  These  effects  will  not  be  found  unless  the  sewage 
in  question  is  of  a  highly  corrosive  character,  and  where  there  is 
no  free  air  supply  to  induce  rapid  oxidation. 

Here,  as  in  previous  cases,  disintegration  will  not  occur  in  a 
dense  and  waterproof  concrete,  only  slight  surface  injury  being 
possible.  (See  Chapter  XXX.) 

The  following  comments  on  this  subject  appeared  in  Engineer- 
ing Contracting  of  June  15,  1910: 

"  Failures  recorded  chiefly  in  Montana  and  Colorado  demon- 
strate with  certainty  that  concrete  can  be  completely  disintegrated 
by  alkali  water  and  that  no  brand  of  cement  is  less  susceptible  to 
damage  than  others.  They  also  show  conclusively  two  other  facts: 
(i)  That  porosity  of  the  concrete  increases  the  chances  of  disinte- 
gration and,  (2)  that  porous  brick  and  porous  stone  suffer  equally. 

"The  alkali  solution  must  penetrate  the  concrete  if  it  is  to  be 
dangerous.  It  is  known,  however,  as  certainly  as  may  be,  that  the 
condition  of  porosity  is  essential  to  the  disintegrating  action  of  alkali 
whether  the  material  be  concrete  or  brick  or  stone.  The  obvious 
preventative  is,  then,  to  provide  against  the  penetration  of  the  con- 
crete by  the  destructive  salt -laden  water,  and  this  brings  us  around 
to  the  undetermined  problem  of  making  an  impermeable  concrete. 

"There  are  cases  where  an  acid  water  or  an  acid  sewage  has 
destroyed  a  cement  structure  by  contact,  and  also  cases- where  such 
a  contact  in  no  way  injured  the  structure,  but  where  serious  injury 

[32] 


Concrete  and  Its  Properties 

has  been  caused  by  gases  above  the  waters  after  escaping  from  them; 
so  that,  in  one  case  the  cement  has  deteriorated  only  below  the  water 
surface,  and  in  the  other  it  has  deteriorated  only  above  it. 

"The  preventative,  as  in  the  former  case,  if  practicable,  is  to  ex- 
clude the  objectionable  element,  or  to  give  the  cement  a  protective 
coating  or  lining. 

"The  effects  of  the  gases  produce  an  entirely  different  condition. 
The  most  serious  of  these  is  that  of  the  sulphuretted  hydrogen  which 
may  be  converted  into  sulphuric  acid  in  the  sewer  above  the  water. 
This  acid  transformed  the  carbonate  of  lime  in  the  cement  joints 
into  sulphate  of  lime,  a  soft,  friable  gypsum,  which  gradually  caused 
the  complete  destruction  of  the  binding  quality  of  the  mortar. 

"In  this  case,  no  doubt,  a  good  forced  ventilation  might  have 
prevented  the  formation  of  sulphuric  acid,  or  the  sewer  might  have 
been  given  a  vitrified  lining,  or  it  may  be  possible  to  apply  a  coating 
which  will  protect  sewers  from  this  sort  of  destruction. 

"Structures  have  been  protected  against  injury  from  sulphuric 
acid  and  other  organic  acids  in  peat  or  similar  soils  by  a  complete 
covering  of  three  layers  of  asphalt  paper. 

"The  foregoing  data  seem  to  indicate  the  following  inferences: 

"  i.  When  the  immediate  agent  of  destruction  is  carried  by  water, 
disintegration  will  be  found  below  the  permanent  water  surface.  If 
such  water  is  flowing  inside  of  a  structure,  as  in  a  sewer  (acid  or 
alkali  factory  waste),  the  disintegration  will  be  inside  and  as  far  as 
the  water  penetrates  the  material.  If  the  water  is  ground-water  in 
alkali  soil,  swamp,  or  peat,  the  disintegration  will  be  on  the  outside 
and  chiefly  between  high  and  low  ground-water  levels,  and  may 
penetrate  porous  material  toward  the  inside  of  the  structure. 

"  2.  When,  on  the  other  hand,  the  agent  of  destruction  is  caused 
by  gases  (generally  sulphuretted  hydrogen),  arising  from  waters, 
whether  on  the  outside  or  the  inside  of  a  structure,  the  disintegration 
will  take  place  above  the  permanent  water  surface." 

Strength  of  Concrete. — The  strength  of  concrete  as  has  already 
been  stated,  depends  upon  the  mixture  employed,  character  of 
mixing,  care  in  placing  and  protecting  the  work,  and  upon  the  age 
of  the  concrete. 

The  strength  of  plain  concrete  is  principally  in  resisting  com- 
pression or  crushing  forces,  and  in  this  direction  it  can  withstand 

*  [33] 


Handbook  for  Cement  and  Concrete  Users 

very  heavy  loads,  500  Ibs.  per  square  inch  being  an  average 
safe  working  value,  which  is  used  in  computations  for  various 
purposes. 

While  it  possesses  a  good  deal  of  resistance  to  tensile  stresses, 
it  is  not  economical  to  employ  concrete  when  such  stresses  are  to  be 
taken  care  of.  As  will  be  seen  later,  steel  performs  this  duty 
admirably  and  in  the  combination  of  the  two,  an  excellent  new 
material  results,  possessing  the  combined  virtues  of  both. 

The  loads  which  can  safely  be  placed  on  concrete  structures 
of  various  kinds  are  discussed  in  the  respective  chapters  of  the  book. 

In  1904  and  1905  the  Aqueduct  Commissioners  of  New  York 
had  an  elaborate  series  of  tests  made  on  the  strength  of  concrete, 
and  the  following  laws  were  deduced  relative  to  strength  and  per- 
meability of  concrete.  \ 

1.  The  largest  size  storjj?  makes  the  strongest  concrete  under 
both  compression  and  transverse  loading,  i.e.,  an  aggregate  whose 
maximum  size  stone  is  2  1/4  in.  diameter  gives  stronger  concrete 
than  an  aggregate  with  i  in.  maximum  size,  and  the  i-in.  stone  gives 
a  stronger  concrete  than  a  i/2-in.  stone. 

2.  The  largest   stone   makes  the   densest   concrete.     Concrete 
made  with  stone  having  a  maximum  diameter  of  2  1/4  in.  is  notice- 
ably denser  than  that  with  i -in.  stone,  and  this  is  denser  than  that 
with  i/2-in.  stone. 

3.  Round  material  like  gravel  gives  under  similar  conditions  a 
denser  concrete  than  broken  stone. 

4.  Sand  produces  a  denser  concrete  than  screenings  when  used 
with  the  same  proportions  of  stone  and  cement. 

5.  Cement,  sand,  and  gravel  concrete  is  stronger  than  concrete 
of  cement,  screenings,  and  broken  stone,  probably  because  of  this 
greater  density.     Concrete  of  cement,  sand,  and  broken  stone,  how- 
ever, is  found  to  be  stronger  than  concrete  of  cement,  sand,  and 
gravel,  although  the  latter  mix  is  denser,  thus  indicating  a  stronger 
adhesion  of  cement  to  broken  stone  than  to  gravel. 

6.  In  ordinary  proportioning  with  two  given  kinds  of  aggregates 
and  a  given  percentage  of  cement,  the  densest  and  strongest  mixture 
is  attained  when  the  volume  of  the  mixture  of  sand,  cement,  and 
water  is  so  small  as  to  just  fill  the  voids  in  the  stone.     In  other 
words,  in  practical  construction  use  as  small  a  proportion  of  sand 

.134] 


Concrete  and  Its  Properties 

and  as  large  a  proportion  of  stone  as  is  possible  without  producing 
visible  voids  in  the  concrete. 

7.  Permeability  or  rate  of  flow  through  concrete  is  less  as  the 
per  cent  of  cement  is  increased,  and  in  very  much  larger  inverse 
ratio. 

8.  Rate  of  flow  is  less  as  the  maximum  size  of  the  stone  is  greater. 
Concrete  with  maximum  size  stone  of  2  1/4  in.   diameter  is  in 
general  less  permeable  than  one  with  i-in.  diameter    maximum 
stone,  and  this  is  less  permeable  than  one  with  i/2-in.  stone. 

9.  Concrete  of  cement,  sand,  and  gravel  is  less  permeable — 
that  is,  the  rate  of  flow  is  less — than  concrete  of  cement,  screenings, 
and  broken  stone. 

10.  Concrete  of  mixed  broken  stone  and  sand  is  more  permeable 
than  concrete  of  gravel  and  sand,  and  less  permeable  than  concrete 
of  broken  stone  and  screenings,  which  indicates  that  for  water- 
tightness  less  cement  is  required  with  rounded  sand  and  gravel  than 
with  broken  stone  and  screenings. 

11.  The  rate  of  flow  decreases  materially  with  age. 

12.  Rate  of  flow  increases  nearly  uniformly  with  the  increase  in 
pressure. 

13.  Rate  of  flow  increases  as  thickness  of  concrete  decreases, 
but  in  a  much  larger  inverse  ratio. 


[35] 


CHAPTER  V 

SAND,    BROKEN    STONE,    AND    GRAVEL    FOR 
CONCRETE 

Selection  of  Sand. — Tests  for  Sand. — Washing  Sand. — Mixture  of  Bank  Sand  and 
Gravel. — Broken  Stone. — Gravel. 

THE  importance  of  selecting  good  aggregates  for  concrete  is 
second  only  in  importance  to  the  selection  of  cement,  forming  as  it 
does  by  far  the  greater  part  of  the  structure.  The  gradation  in 
size,  proportioning,  etc.,  of  these  materials,  which  is  treated  later, 
have,  as  has  been  seen,  an  important  bearing  upon  the  density  and 
economy  of  the  work  and  all  reasonable  means  should  be  taken  to 
secure  as  good  material  as  is  available. 

Selection  of  Sand. — The  value  of  sand  for  concrete  depends 
largely  on  its  coarseness,  graduation  in  size  of  the  grains,  and  clean- 
liness. Fine  sand  contains  more  voids,  more  surfaces  to  coat,  and 
requires  more  cement  and  water  than  coarse  sand. 

The  sharpness  of  the  grains  of  sand  has  little  to  do  with  its 
value.  It  has  commonly  been  supposed  that  sand  should  be  sharp. 
This,  however,  is  one  of  the  theories  which  have  been  exploded. 
In  fact,  there  are  many  arguments  in  favor  of  coarse,  round-grain 
sand.  Compactness  is  what  is  desired,  giving  density  to  the  mortar; 
round  grains  compact  more  readily  than  sharp  grains,  and  the 
cement  will  cling  to  the  surface  of  round  grains  as  well  as  sharp 
grains,  the  character  of  the  surface  being  identical.  Sharp  sand  is 
only  of  value  as  indicating  a  silicious  sand. 

Good  sand  cannot  be  easily  denned,  or  an  inflexible  specification 
written,  as  sands  of  various  properties  may  make  equally  good 
concrete.  All  things  being  equal,  a  coarse  sand  containing  a  large 
percentage  of  coarse  particles  is  far  superior  to  a  fine  sand  in  which 
few  coarse  particles  are  present. 

The  best  sand  is  that  which,  when  mixed  with  cement  and 
water  in  the  required  proportions  by  weight,  produces  the  least 
volume  of  mortar.  Economy  can  be  practised  in  the  matter  of  the 
selection  of  sand.  It  will  nearly  always  pay  the  concrete  con- 

136] 


Sand,  Broken  Stone,  and  Gravel  for  Concrete 

structor  to  haul  sand  even  from  a  considerable  distance,  paying  a 
higher  price,  provided  he  cannot  get  a  sand  in  the  immediate  locality 
of  the  work,  which  sand  is  so  graduated  in  size  of  grains  as  to  give 
the  greatest  density. 

Sand  containing  vegetable  matter  is  of  doubtful  quality,  as  a 
small  quantity  may  sometimes  prevent  hardening.  The  kind  of 
impurity  is  really  of  more  importance  than  the  quantity. 

How  to  Test  for  a  Clean  Sand.* — Two  rough  tests  are  as  follows: 
(a)  Pick  up  a  double  handful  of  moist  sand  from  the  bank;  open 
the  hands,  holding  them  with  the  thumbs  up;  rub  the  sand  lightly 
between  the  hands,  keeping  them  about  1/2  inch  apart,  allowing 
the  sand  to  slip  quickly  between  them.  Repeat  this  operation  five 
or  six  times,  then  rub  the  hands  lightly  together  so  as  to  remove 
the  fine  grains  of  sand  which  adhere  to  them,  and  examine  to  see 
whether  or  not  a  thin  film  of  sticky  matter  adheres  to  the  fingers; 
if  so,  do  not  use  the  sand,  for  it  contains  loam.  A  further  test  is  to 
scrape  some  of  this  matter  from  the  fingers  on  the  end  of  a  penknife 
and  take  a  little  of  it  between  the  teeth.  If  it  does  not  feel  gritty 
or  sharp  it  indicates  vegetable  loam,  which  is  bad.  Do  not  use 
this  sand,  or  if  no  other  can  be  obtained  test  it  further  to  make  sure 
that  there  is  not  sufficient  loam  present  to  prevent  the  cement  from 
getting  thoroughly  hard. 

The  sand  for  the  test  given  above  must  be  moist,  just  as  it 
comes  from  the  bank.  When  dry  the  dirt  will  not  stick  to  the 
fingers,  hence  this  test  cannot  be  used.  Some  idea  can  be  obtained, 
however,  by  the  appearance  of  the  sand,  even  if  it  is  dry.  If  it  looks 
"dead,"  an  appearance  which  is  caused  by  the  particles  of  dirt 
sticking  in  little  lumps  to  the  grains  of  sand,  sometimes  also  making 
the  grains  of  sand  stick  together  in  little  bunches  when  picked  up, 
it  is  almost  a  sure  sign  of  vegetable  matter,  and  the  sand  should 
not  be  used.  Fine  roots  in  a  sand  will  also  indicate  the  presence  of 
vegetable  matter. 

(b)  Make  up  two  6-inch  cubes  of  concrete,  using  the  same 
cement  and  the  same  sand  and  gravel  or  stone  as  will  be  used  in 
the  structure  to  be  built,  and  mixing  them  in  the  same  proportion 

*  From  "  Concrete  Construction  about  the  Home  and  on  the  Farm,"  published 
by  The  Atlas  Portland  Cement  Co. 

[37] 


Handbook  for  Cement  and  Concrete  Users 

and  of  the  same  consistency.     Keep  one  block  in  the  air  out  of 
doors  for  7  days  and  the  other  in  a  fairly  warm  room. 

The  specimen  in  the  warm  room  should  set  so  that  on  the  follow- 
ing day  it  will  bear  the  pressure  of  the  thumb  without  indentation, 
and  it  should  also  begin  to  whiten  out  at  this  early  period.  The 
specimen  out  of  doors  should  be  hard  enough  to  remove  from  the 
moulds  in  24  hours  in  ordinary  mild  weather,  or  48  hours  in  cold, 
damp  weather.  At  the  end  of  a  week,  test  both  blocks  by  hitting 
them  with  a  hammer.  If  the  hammer  does  not  dent  them  under 


F/ne 


Trough  to  run  off "• dirty  wafer 
Trough  /o  6e  //nect  wjfh  Sarrecf/ja/zer 

FIG.  6.— Washing  Trough  for  Sand  and  Gravel. 

light  blows,  such  as  would  be  used  for  driving  tacks,  and  the  blocks 
sound  hard  and  are  not  broken  under  medium  blows,  the  sand,  as  a 
general  rule,  can  be  used. 

How  to  Wash  Sand. — Sand  cannot  be  washed  simply  by  wetting 
the  pile  of  sand  with  a  hose,  for  this  only  washes  or  transfers  the 
dirt  to  a  lower  part  of  the  pile.  Sand,  provided  it  is  not  too  fine, 
can  be  satisfactorily  washed,  however,  by  making  a  washing  trough. 
For  sands  a  screen  with  30  meshes  to  the  linear  inch  is  necessary  to 
prevent  the  good  particles  from  passing  through  it.  This  must  be 
supported  by  cleats  placed  quite  near  together,  or  it  will  break 
through.  The  sand  is  shoveled  on  to  the  upper  end  of  the  trough 
by  one  man,  while  another  one  can  wash  it  with  a  hose.  The  flow 
of  water  will  wash  the  sand  down  the  incline,  and  as  the  sand  and 
water  pass  over  the  screen  the  dirty  water  will  drain  off  through  the 
screen,  leaving  the  clean  sand  for  use.  By  this  arrangement  the 

[38] 


Sand,  Broken  Stone,  and  Gravel  for  Concrete 

dirt  which  is  washed  out  cannot  in  any  way  get  mixed  with  the  clean 
sand. 

Natural  Mixtures  of  Bank  Sand  and  Gravel. — Very  often  the 
sand  and  gravel  found  in  a  bank  are  used  by  inexperienced  people, 
just  as  it  is  found  without  regard  to  the  proportions  of  the  two 
materials.  This  may  be  all  right  in  some  cases,  but  generally  there 
is  too  much  sand  for  the  gravel  or  stone,  so  that  the  resulting  con- 
crete is  not  nearly  as  strong  as  it  would  be  if  the  proportions  between 
the  sand  and  gravel  were  right.  It  is  better  then  to  screen  the  sand 
from  the  gravel  through  a  i/ 4-inch  sieve,  and  then  mix  the  materials 
in  the  right  proportions,  using  generally  about  half  as  much  sand 
as  stone.  By  so  doing  a  leaner  mix  can  be  used  than  where  the 
sand  and  gravel  are  taken  from  the  bank  direct.  The  cost  of  the 
cement  saved  will  more  than  pay  for  the  extra  labor  required  to 
screen  the  material.  For  example:  Using  even  a  very  good  gravel 
bank,  a  mixture  one  part  cement  to  four  parts  natural  gravel  must 
be  employed  instead  of  one  part  cement  to  two  parts  sand  to  four 
parts  of  screened  gravel.  So  much  more  cement  is  thus  required 
with  the  natural  gravel  that  a  saving  of  one  bag  of  cement  in  every 
seven  is  made  by  screening  and  remixing  in  the  right  proportion. 

Crusher  Screenings. — Screenings  from  broken  stone  make  an 
excellent  fine  aggregate,  which  can  be  substituted  for  sand  unless 
the  stone  is  very  soft,  shelly,  or  contains  a  large  percentage  of 
mica. 

Broken  Stone  for  Concrete.*— The  purpose  for  which  the  concrete 
is  intended  must  always  influence  the  selection  of  the  stone.  For 
a  very  strong  concrete,  a  hard  stone  without  any  surface  scale  is 
necessary;  a  rich  mortar  will  not  entirely  counterbalance  a  deficiency 
in  the  strength  of  the  stone.  For  a  medium  strong  concrete  the 
hardest  stone  need  not  be  insisted  upon,  but  rather  one  to  which 
the  mortar  will  best  adhere,  such  as  some  of  the  limestones.  For 
fireproof  construction  some  of  the  limestones  and  rocks  containing 
feldspar  should  be  avoided;  good  boiler  furnace  cinders  have 
proved  best  for  fire-resisting  concrete. 

For  all  classes  of  concrete,  stone  breaking  in  cubical  form  is 
far  better  than  one  breaking  in  flat  layers  such  as  shale  or  slate,  it 

*  Condensed  from  paper  on  "Concrete  Aggregates,"  by  Albert  Moyer. 

[39] 


Handbook  for  Cement  and  Concrete  Users 

being  almost  impossible  to  ram  or  tamp  such  stone  into  as  dense 
and  compact  a  mass  as  that  breaking  in  cubical  fracture. 

The  size  of  the  stone  aggregates  depends  on  the  purpose  for 
which  the  concrete  is  to  be  used.  For  large  masses  of  concrete, 
2-1/2 -inch  stone  is  usually  considered  the  maximum  size,  but  for 
12-inch  walls  and  the  usual  class  of  concrete  construction,  3/4  inch 
will  be  found  sufficiently  large.  Quarry  tailings,  etc.,  in  crushed 
stone,  are  not  a  detriment,  as  is  commonly  supposed,  but  in  fact  a 
decided  advantage,  for  the  reason  that  the  voids  are  thus  reduced, 
giving  greater  density  and  consequently  greater  strength. 

Material  which  is  foreign  to  the  stone,  such  as  vegetable  mould, 
scale,  or  loam,  which  cling  to  the  surface  will  reduce  the  strength 
of  the  concrete.  Numerous  tests  conducted  during  the  last  several 
years  by  competent  engineers  have  shown  that  clay  in  small  pro- 
portions, not  over  15  per  cent,  when  well  mixed  in  the  mortar,  does 
not  reduce  the  strength  of  the  concrete;  in  fact,  tests  have  shown 
that  the  strength  has  been  increased.  This  applies  particularly 
to  the  leaner  mixtures.  If  carefully  mixed,  therefore,  the  clay  will 
not  cling  to  the  stone,  but  will  become  part  of  the  mortar,  and  in 
testing  for  proportions  of  stone,  sand,  and  cement,  the  amount  of 
clay  present  should  be  figured  as  part  of  the  mortar  and  not  as  part 
of  the  stone. 

Gravel  for  Concrete. — Gravel  is  often  superior  to  broken  stone, 
being  usually  found  graded  from  coarse  to  fine;  the  roundness  of 
the  pebbles  lends  aid  to  compactness.  It  is  not  likely  to  bridge 
and  leave  holes  in  the  concrete.  The  percentage  of  voids  is  usually 
less  than  in  broken  stone;  the  quartz  pebbles  are  harder,  stronger, 
and  less  liable  to  fracture. 

Sandstone  pebbles  are  not  considered  as  good  as  the  better 
grades  of  crushed  stone.  The  usual  argument  against  gravel  is 
that  the  mortar  is  not  supposed  to  adhere  as  well  to  the  surface 
as  to  that  of  freshly  broken  stone.  This  is  one  of  the  theories  which 
is  practically  due  to  the  appearance  of  the  surface  to  the  eye  or 
touch;  the  adhesion  of  mortar  to  limestone  of  a  smooth  surface, 
may  be  far  greater  than  to  sand  stone  or  rougher  materials.  If 
roughness  was  the  only  requirement  for  adhesion  it  would  seem 
impossible  to  cement  together  two  pieces  of  glass. 

From  the  standpoint  of  durability,  gravel  must  be  superior  to 


Sand,  Broken  Stone,  and  Gravel  for  Concrete 

stone  for  the  reason  that,  by  the  laws  of  the  survival  of  the  fittest* 
and  by  process  of  elimination,  nature  has  supplied  us  with  the  most 
durable.  Short-time  tests  for  compression  strength  usually  show 
broken  stone  concrete  to  be  superior,  but  long-time  tests  of  from 
six  months  to  a  year  show  gravel  concrete  on  an  average  to  be  equal 
if  not  stronger.  In  construction  work  where  tensile  or  other  stresses 
are  to  be  cared  for,  as  may  occur  in  reinforced  concrete,  crushed 
gravel  should  be  used.  The  cement  will  adhere  more  readily  to 
crushed  than  to  the  rounded,  polished  surface  of  the  gravel. 


CHAPTER  VI 

HOW  TO  PROPORTION  THE  MATERIALS 

Nature  of  the  Problem. — Voids  in  Concrete. — Methods  of  Proportioning. — Tables 

for  Proportioning. 

Nature  of  the  Problem. — A  great  deal  of  study  has  been  given 
to  the  question  of  proportioning  the  materials  of  concrete,  and  most 
of  the  study  has  been  directed  to  one  end;  viz.,  to  find  a  mixture 
that  will  give  the  maximum  density  and  strength  with  a  minimum 
amount  of  cement.  The  difficulties  in  arriving  at  any  definite 
rules  for  obtaining  this  result  arise  from  the  great  variation  in  the 
various  elements  affecting  the  work,  no  two  materials  being  exactly 
alike,  and  rules  deduced  from  one  set  of  experiments  being  of  very 
doubtful  value  when  applied  to  other  conditions.  Although  a  good 
deal  of  care  in  proportioning  is  warranted,  to  obtain  the  best  mix 
with  any  given  material,  too  great  refinement  is  unnecessary  and 
the  theoretical  methods  which  have  been  gone  into  with  such  great 
detail  in  many  of  the  books  on  concrete  work  have  more  of  an  aca- 
demic interest  than  a  practical  value. 

The  principal  thing  to  bear  in  mind  in  order  to  obtain  the  densest 
possible  mixture  is  to  eliminate  the  voids  in  the  concrete  mass, 
and  to  do  this,  it  is  desirable  that  the  sand  and  gravel  be  well  graded 
from  coarse  to  fine  and  enough  cement  be  used  to  obtain  a  rich 
mixture.  Plenty  of  water,  to  obtain  a  wet  mix,  should  be  employed, 
as  water  will  drive  out  the  air  entrained  between  the  particles  of 
the  aggregates.  The  density,  strength,  and  watertightness  of 
concrete  will  be  increased  in  accordance  with  the  richness,  variation 
in  size  of  aggregate,  and  with  the  plasticity  of  the  mixture.  Mix 
rich  and  mix  wet  to  obtain  the  best  work. 

The  question  of  proportioning  is,  of  course,  also  dependent  upon 
the  use  to  which  the  concrete  is  to  be  put  and  in  many  locations 
density  and  strength  may  not  be  the  prime  requisites,  and  then  a 
very  small  percentage  of  cement  will  suffice  to  obtain  a  hardened 
mass;  as  low  as  5  per  cent  has  given  a  strong  concrete, 

[42] 


How  to  Proportion  the  Materials 

Voids  in  Concrete. — American  engineers  proportion  concrete 
mixtures  by  measure,  thus  a  1:2:4  concrete  is  composed  of  i  volume 
of  cement,  2  volumes  of  sand,  and  4  volumes  of  broken  stone. 
Both  the  sand  and  the  coarse  aggregates  employed  for  concrete 
contain  voids  or  empty  spaces  between  their  particles.  In  a  perfect 
mixture  the  cement  would  fill  the  voids  in  the  sand  and  coat 
each  grain,  while  the  sand  with  its  coating  of  cement  would  fill 
the  voids  in  the  aggregate  and  also  cover  each  stone  with  a  film  of 
mortar. 

In  practice,  it  is  impossible  to  fill  all  of  the  voids  in  concrete. 
In  the  first  place,  the  cement  and  sand  cannot  be  perfectly  dis- 
tributed, and  in  the  second  place,  the  water  used  in  the  mixing 
causes  the  sand  to  swell,  thus  increasing  the  voids  about  10  per  cent. 
This  swelling  is  due  to  a  film  of  water  between  the  grains,  and  this 
film  cannot  be  entirely  displaced  by  the  cement.  When  the  water 
evaporates  after  a  wall  of  concrete  has  set,  voids  always  remain 
throughout  the  mass,  and  some  shrinkage  of  the  mass  occurs. 

A  rich  mixture  is  obtained  when  the  cement  is  somewhat  in 
excess  of  the  quantity  that  would,  theoretically,  be  sufficient  to  fill 
the  voids  in  the  sand.  Sand  and  gravel  contain  from  30  to  50  per 
cent  of  voids,  while  the  voids  in  broken  stone  range  from  40  to  50 
per  cent. 

The  proportion  of  voids  may  be  approximately  determined  in 
either  sand  or  broken  stone  in  the  following  way  : 

Wet  the  loose  aggregate  thoroughly;  fill  a  vessel  of  known 
capacity  with  the  material,  and  then  pour  in  all  the  water  the  vessel 
will  contain.  Measure  the  volume  of  water  required  and  divide 
this  by  the  volume  of  the  vessel.  The  quotient  represents  the 
proportion  of  voids. 

Method  of  Proportioning. — The  ordinary  mixture  for  watertight 
concrete  is  about  i  :  2\  :  4%  which  requires  1.32  barrel  of  cement 
per  cu.  yd.  of  concrete.  The  most  scientific  method  for  proportion- 
ing the  ingredients  is  that  known  as  the  Mechanical  Analysis. 
In  this  method  the  available  materials,  including  the'  cement,  are 
separated  into  various  sizes  by  means  of  a  series  of  sieves.  Curves 
are  then  plotted  on  cross-section  paper  which  indicate  the  per- 
centages of  the  whole  mass  that  pass  the  several  sieves.  From  a 
study  of  these  curves,  the  proportions  of  the  different  ingredients 

[43] 


Handbook  for  Cement  and  Concrete  Users 

are  determined.  This  method  is,  however,  not  available  in  the 
usual  course  of  concrete  work. 

In  hand-mixing,  cement  is  generally  measured  by  specifying 
the  number  of  bags  to  a  batch.  Machine  mixers  frequently  have 
automatic  measuring  devices.  When  removed  from  the  bag  or 
barrel,  cement  occupies  about  15  per  cent  more  space  than  when  in 
the  original  package;  or  a  i  :  2  : 4  mixture  measured  by  counting  the 
number  of  bags  will  be  1 5  per  cent  richer  than  a  1:2:4  mixture, 
which  is  proportioned  by  measuring  the  cement  loose.  Hence  in 
determining  the  proportions,  the  methods  of  measuring  the  cement 
should  be  considered  and  specifications  should  clearly  provide  how 
this  shall  be  done. 

Volume  of  Barrel  of  Cement. — The  difference  between  the 
volume  of  a  barrel  of  cement  when  measured  packed  and  loose, 
and  variations  in  size  and  weight  have  been  subjects  of  extended 
controversy  and  often  bitterness  between  engineer  and  contractor, 
and  has  resulted  in  much  friction  and  litigation.  The  tendency 
now  is  to  fix  an  arbitrary  but  average  value  for  the  volume  of  the 
cement  barrel  as  a  standard,  and  have  this  used  as  a  basis  on  all 
concrete  work.  The  value  of  4  cu.  ft.  to  the  barrel  is  preferred, 
the  actual  volume  being  about  3.75  cu.  ft.  packed  and  4.2  cu.  ft. 
loose.  The  fixing  of  such  a  standard  of  value  is  highly  de- 
sirable, and  would  be  of  great  benefit  to  engineers  and  contractors 
alike. 

Proportions  by  Formula. — A  number  of  formulas  have  been 
introduced  for  proportioning  the  sand,  cement  and  stone  and  it  is 
worth  the  cement  user's  while  to  take  note  particularly  of  the  one 
here  given,  as  it  is  exceedingly  simple  and  may  save  much  trouble 
in  proportioning.  While  proportioning  by  formula  is  not  employed 
as  frequently  as  proportioning  by  rule  of  thumb,  the  method  has 
been  employed  to  work  out  some  excellent  tables  for  proportioning 
concrete  and  these  tables  are  extremely  useful  in  estimating  the 
amount  of  cement  required  on  any  particular  job  as  well  as  for 
other  construction  purpose. 

The  simplest  formula  for  this  purpose  is: 

27  s 

~ng  21  g 

[44] 


How  to  Proportion  the  Materials 


B  =  number  of  barrels  of  cement  per  cu.  yd.  of  concrete. 
n  =  number  of  cubic  feet  in  barrel  of  cement  as  specified. 
g  =  number  of  parts  of  gravel  to  i  part  cement  as  specified. 
C  =  number  of  cubic  feet  of  sand  per  cu.  yd.  of  concrete, 
s  =  number  of  parts  of  sand  to  i  part  of  cement  as  specified. 
This  formula  assumes  that  the  voids  in  the  gravel   are  filled  by 
the  sand  and  the  voids  in  the  sand  are  filled  by  the  mortar,  and 
therefore  the  results  are  approximate. 

Thus  for  a  i :  2 :  4  concrete,  when  i  bbl.  cement  is  specified  as 
4  cubic  feet, 


B  = 


27 


4X4 


1.7  bbls.  cement. 


C  =  27XY~==I3-5  cubic  feet  sand. 

2 

The  following  table  was  computed  by  Gillette's  formula,  giving 
the  quantities  of  cement,  sand,  aggregate,  and  water  required  to 
produce  one  cubic  yard  of  wet  concrete : 

TABLE  II. — INGREDIENTS    IN  ONE  CUBIC  YARD  OF  CONCRETE. 
Voids  in  Sand,  40  per  cent.       Voids  in  Stone,  45  per  cent. 


Proportions  by  Volume. 

1:2:4 

1:2^:4$ 

1:2:5 

1:2*15 

^3:5 

i:3:6 

Per  Cent  of  Voids  in  Concrete.  .  .  . 

10% 

8% 

12% 

12% 

12% 

14% 

Bbls.  Cement:  Measured   Packed 

per  cu.  yd.  of  Concrete,  i  bbl  .  = 

•7  8  cu  ft 

I    4.6 

I    32 

i  .2tr 

I    2O 

I    .I^ 

i  .00 

Cu.  yds.  Sand  per  cu.  yd.  Concrete 

.41 

.46 

•35 

.42 

•48 

.42 

Cu.  yds.  Stone  per  cu.  yd  Concrete. 

.82 

.83 

.88 

.84 

.80 

.84 

Approximate  per  cent  of  water  for 

wet  mixtures  

IT.% 

12*% 

17% 

12*% 

12% 

12% 

In  Table  II,  the  approximate  amount  of  water  required  for  a 
wet  mixture  is  expressed  as  a  percentage  of  the  combined  weight 
of  sand  and  cement.  These  percentages  are,  however,  only 
approximate.  More  water  is  required  in  dry  than  in  moist  atmo- 
spheres, and  more  in  summer  than  in  winter.  A  wetter  mixture  is 
also  required  when  the  material  cannot  be  tamped.  While  a  dry 
mixture  is  theoretically  the  stronger  when  carefully  deposited  and 

[45] 


Handbook  for  Cement  and  Concrete  Users 

well  tamped,  yet  a  wet  mixture  is  more  frequently  employed  be- 
cause stronger  under  working  conditions.  Wet  mixtures  flow 
readily  into  the  corners  and  angles  of  the  forms  and  between  and 
around  the  reinforcing  bars,  with  only  a  small  amount  of  puddling 
and  slicing. 


TABLE    III. — MATERIALS   FOR    ONE    CUBIC    YARD   COMPACT 
PLASTIC  MORTAR  BASED  ON  BARREL  OF  3.8  CUBIC  FEET. 

From  "  Concrete  Plain  and  Reinforced,"  by  Taylor  &  Thompson. 


RELATIVE  PROPORTIONS  BY 
PARTS. 

RELATIVE  PROPORTIONS  BY 
VOLUME. 

Packed 
Cement 
Barrels. 

Loose  Sand 
Cubic  Yard. 

Cement. 

Sand. 

Cement 
Barrel. 

Sand 
Cubic  Feet. 

0 

8.31 

i 

1.9 

6-73 

0.47 

I 

3-8 

5.01 

0.71 

Ji 

5-7 

4.00 

0.84 

2 

7-6 

3-32 

o-93 

2£ 

I 

9-5 

2.84 

i  .00 

3 

i 

11.4 

2.48 

1.05 

3* 

I 

J3-3 

2  .20 

i.  08 

4 

i 

15  .2 

.98 

i  .11 

4l 

17.1 

.80 

1.14 

5 

19  .0 

•65 

1.16 

5l 

20  .9 

•52 

1.18 

6 

22.8 

.41 

1.19 

6| 

24.7 

•32 

I.  21 

7 

26.6 

•23 

I  .21 

7i 

28-5 

.16 

I  .22 

8 

30-4 

.10 

1.24 

[46] 


CHAPTER  VII 

HOW  TO  MIX  AND  PLACE  CONCRETE 

Methods  of  Mixing. — How  to  Mix  by  Hand. — Materials  Required  for  Two-Bag 
Batch. — Mixing  by  Machine. — Placing  the  Concrete. — Protection  of  Concrete 
After  Placing. — Placing  Concrete  Under  Water. 

THE  proper  mixing  and  placing  of  concrete  is  fully  as  important 
as  is  the  proportioning  of  its  ingredients.  Two  general  methods  are 
in  use : 

(i)  Hand  mixing;   (2)  Machine  mixing. 

MIXING  CONCRETE  BY  HAND 

The  making  and  placing  of  concrete  by  hand  is  divided  into  the 
following  operations : 

1.  Loading  into  barrows,  buckets,  carts,  or  cars,  which  are  used 
to  transport  the  cement,  sand,  and  stone  to  the  mixing  board. 

2.  Transporting  and  dumping  the  materials. 

3.  Mixing  the  materials  by  turning  with  shovels  and  hoes. 

4.  Loading  the  concrete  by  shovels  into  barrows,  buckets,  carts, 
or  cars. 

5.  Transporting  the  concrete  to  piace. 

6.  Dumping,  spreading,  and  ramming. 

Hand  mixing  is  used  for  small  batches.  The  stone  and  sand 
are  measured  in  bottomless  boxes  and  the  cement  by  counting  the 
number  of  bags  to  a  batch,  each  bag  representing  a  quarter  of  a 
barrel. 

As  hand  mixing  is  so  largely  employed  throughout  the  country 
on  the  smaller  jobs,  the  following  detailed  description  is  given,  and 
if  carefully  followed,  any  intelligent  person  should  be  able  to  secure 
a  satisfactory  mix.  In  this  description  *  we  have  taken  as  a  basis  a 
" Two-bag  Batch"  of  i :  2 : 4  concrete.  The  amount  of  material  re- 
quired is  given  in  the  Tables  IV  and  V. 

*  This  description  is  adapted  from  Bulletin  No.  20,  published  by  American  Associa- 
tion of  Portland  Cement  Manufacturers. 

[47] 


Handbook  for  Cement  and  Concrete  Users 

Concrete  Board. — A  concrete  board  for  two  men  should  be 
9  feet  x  10  feet.  Make  it  out  of  i-inch  boards,  10  feet  long,  surfaced 
on  one  side,  using  five  2  inch  x  4  inch  x  9  foot  cleats  to  hold  them 
together.  If  i  inch  x  6  inch  tongue-and-groove  roofers  can  be 
obtained,  they  will  do  very  nicely  if  fairly  free  from  knots.  The 
object  of  the  surfaced  board  is  to  make  the  shovelling  easy.  The 
boards  are  so  laid  as  to  enable  the  shovelling  to  be  done  with,  and  not 
against,  the  cracks  between  the  boards.  The  boards  must  be  drawn 
up  close  in  nailing  so  that  no  cement  grout  will  run  through  while 
mixing. 

Knot-holes  may  be  closed  by  nailing  a  strip  across  them 
on  the  under  side  of  the  board.  It  is  a  good  precaution  against 
losing  cement  grout  to  nail  a  2  inch  x  2  inch  or  2  inch  x  4  inch  piece 
around  the  outer  edge  of  the  board.  Often  2-inch  planks  are  used 
in  making  concrete  boards,  but  these  are  unnecessarily  heavy  and 
very  cumbersome  to  move. 

Placing  the  Concrete  Board. — The  concrete  board  is  a  manu- 
facturing plant,  and  the  advantages  of  its  location  should  be  care- 
fully considered.  Generally  it  is  best  placed  as  close  as  possible 
to  the  forms  in  which  the  concrete  is  to  be  deposited,  but  "  local 
conditions"  must  govern  this  point.  Pick  a  place  giving  plenty  of 
room,  near  the  storage  piles  of  sand  and  stone  (or  pebbles).  Block 
up  your  concrete  board  level,  so  that  the  cement  grout  will  not  run 
off  on  one  side,  and  so  that  the  board  will  not  sag  in  the  middle 
under  the  weight  of  the  concrete. 

Runs. — Do  not  use  any  old  boards  that  are  handy  for  the 
wheelbarrow  runs.  Make  a  good  run,  smooth,  and  at  least  20 
inches  wide  if  much  above  the  ground.  .It  is  surprising  how  this 
one  feature  will  lighten  and  quicken  the  work. 

Tools  and  Plant. — List  of  tools  and  plant  to  be  used  in  mixing, 
giving  sizes,  quantities,  etc. 

Concrete  Board  for  2-Bag  Batch,  9'  x  10'  in  size. 

9  pcs.  f"  X  12"  X  IO'Q",  surfaced  one  side  and  two  edges.     (Any  width  of  plank 
may  be  used;   12"  is  specified  only  for  convenience.) 
5  pcs.  2"  X  4"  X    9'o"  rough. 
2  pcs.  2"  X  2"  X  IO'Q"  rough. 
2  pcs.  2"  X  2"  X    9'o"  rough. 

[48] 


How  to  Mix  and  Place  Concrete 
Concrete  Board  for  4-Bag  Batch,  12'  x  10'  in  size. 

12  pcs.  f"  X  12"  X  ro'o",  surfaced  one  side  and  edges.     (Any  width  of  plank  may 
be  used;   12"  is  specified  only  for  convenience.) 
5  pcs.  2"  X  4"  X  1  2V  rough. 
2  pcs.  2"  X  2"  X  10  V  rough. 
2  pcs.  2"  X  2"  X  i2'o"  rough. 


.  —  2",  2  1/2",  or  3"  plank  10"  or  12"  wide. 
Measuring  Boxes  for  Sand  and  Stone  or  Gravel. 
For  2-Bag  Batch  1:2:4  Mixture  : 

4  pcs.  i"  X  n$  X  2'o"  rough. 
2  pcs.  i"  X  n$"  X  4'o"  rough. 
2  pcs.  i*  X  n$"  X  6V  rough. 

NOTE.  —  The  2  pcs.  4V  long  and  the  2  pcs.  6V  long  have  an  extra  foot  in  length 
at  each  end  to  be  made  into  a  handle. 

For  2-Bag  Batch  1:3:6  Mixture: 

2  pcs.  i"  X  n$"  X  2V 
2  pcs.  i"  X  n$"  X  3V 
2  pcs.  i"  X  1  4"  X  s'o" 
2  pcs.  i"  X  n$"  X  6V 

NOTE.  —  The  2  pcs.  5V  long  and  the  2  pcs.  6V'  long  have  an  extra  foot  in  length 
at  each  end  to  be  made  into  a  handle. 

For  4-Bag  Batch: 

Double  cubic  contents  of  boxes  and  order  lumber  accordingly. 

Shovels.  —  No.  3  square  point. 

Wheelbarrows.  —  At  least  two  necessary  for  quick  work;  sheet- 
iron  body  preferred. 

Rake. 

Water-barrel. 

Water-buckets.  —  2-gallon  size. 

Tamper.  —  4"  x  4"  x  2'6",  with  handles  nailed  to  it. 

Garden    spade    or    "spading"    tool,    as    shown    in    Fig.  13. 

Sand  Screen.  —  Made  by  nailing  a  piece  of  1/4"  mesh  wire  screen 
2  1/2'  x  5'  in  size  to  a  frame  made  of  2"  x  4". 

Mixing.  —  With  the  mixing  board  placed  and  the  "runs"  made, 
the  concrete  plant  is  ready. 

First  load  your  sand  in  wheelbarrows  from  the  sand  pile,  wheel 
on  to  the  "Board,"  and  fill  the  sand-measuring  box,  which  is  placed 

4  [49] 


Handbook  for  Cement  and  Concrete  Users 


about  two  feet  from  one  of  the  lo-foot  sides  of  the  board.  When 
the  sand  box  is  filled,  lift  it  off  and  spread  the  sand  over  the  board  in 
a  layer  3  inches  or  4  inches  thick.  Take  the  two  bags  of  cement  and 
place  the  contents  as  evenly  as  possible  over  the  sand.  With  two  men 
start  mixing  the  sand  and  cement,  each  man  turning  over  the  half 
on  his  side.  Starting  at  his  feet  and  shovelling  away  from  him,  each 
man  takes  a  full  shovel-load,  turning  the  shovel  over.  In  turning 
the  shovel,  do  not  simply  dump  the  sand  and  cement  but  shake  the 
materials  off  the  end  and  sides  of  the  shovel,  so  that  the  sand  and 
cement  are  mixed  as  they  fall.  This  is  a  great  assistance  in  mixing 


FIG.  7. — Homemade  Tools  for  the  Concrete  Worker. 

these  materials.     In  this  way  the  material  is  shovelled  from  one 
side  of  the  board  to  the  other. 

After  the  last  turning,  spread  the  sand  and  cement  out  carefully, 
place  the  gravel  or  stone  measuring  box  beside  it  and  fill  from  the 
gravel  pile.  Lift  off  the  box  and  shovel  the  gravel  on  top  of  the 
sand  and  cement,  spreading  it  as  evenly  as  possible.  With  some 
experience  equally  good  results  can  be  obtained  by  placing  the 
gravel  measuring  box  on  top  of  the  carefully  levelled  sand  and 
cement  mixture,  and  filling  it,  thus  placing  the  gravel  on  top  without 
an  extra  shovelling.  Add  about  three-fourths  the  required  amount 
of  water,  using  a  bucket  and  dashing  the  water  over  the  gravel  on 
top  of  the  pile  as  evenly  as  possible.  Be  careful  not  to  let  too  much 
water  get  near  the  edges  of  the  pile,  as  it  will  run  off,  taking  some 

[50] 


How  to  Mix  and  Place  Concrete 


cement  with  it.  This  caution,  however,  does  not  apply  to  a  properly 
constructed  mixing  board,  as  the  cement  and  water  cannot  get 
away.  Starting  the  same  as  with  the  sand  and  cement,  turn  the 
materials  over  in  much  the  same  way,  except  that,  instead  of  shaking 
the  materials  off  the  end  of  the  shovel,  the  whole  shovel  load  is 
dumped  and  dragged  back  toward  the  mixer  with  the  square  point 
of  the  shovel.  This  mixes  the  gravel 
with  the  sand  and  cement,  the  wet 
gravel  picking  up  the  sand  and  cement 
as  it  rolls  over  when  dragged  back  by 
the  shovel.  Add  water  to  the  dry  spots 
as  the  mixing  goes  on  until  all  the  re- 
quired water  has  been  used.  Turn  the 
mass  back  again,  as  was  done  with  the 
sand  and  cement.  With  experienced 
laborers,  the  concrete  would  be  well 
mixed  after  three  such  turnings ;  but  if  it 
shows  streaky  or  dry  spots,  it  must  be 
turned  again.  After  the  final  turning, 
shovel  into  a  compact  pile.  The  con- 
crete is  now  ready  for  placing. 

Mixing  Natural  Mixture  of  Bank 
Sand  and  Gravel. — Spread  out  the  mixture  of  sand  and  gravel  as 
much  as  the  board  will  readily  permit,  add  enough  water  to  wet 
the  gravel  and  sand  thoroughly,  spread  the  cement  evenly  in  a 
thin  layer  over  the  sand  and  gravel,  and  turn  over,  as  described 
previously,  at  least  three  times,  adding  the  rest  of  the  water  nec- 
essary to  get  the  required  consistency  while  the  materials  are  being 
turned.  It  requires  some  experience  to  work  up  a  natural  mix- 
ture of  bank  sand  and  gravel,  and  if  at  all  doubtful  about  the 
concrete  made  from  it,  first  screen  the  sand  from  the  gravel  and 
then  mix  in  the  regular  way. 

Number  of  Men. — For  the  above  operation  only  two  men  are 
required,  although  more  can  be  used  to  advantage.  If  three  men 
are  available,  let  two  of  them  mix  as  described  above  and  the  third 
man  supply  the  water,  help  mix  the  concrete  by  raking  over  the  dry 
or  unmixed  spots  as  the  two  mixers  turn  the  concrete,  help  load  the 
wheelbarrows  with  sand  and  stone  or  gravel,  etc. 

[SO 


FIG.  8. — Homemade  Con- 
crete Tamper. 


Handbook  for  Cement  and  Concrete  Users 

If  four  men  are  available,  it  is  best  to  increase  the  size  of  the 
batch  mixed  to  a  four-bag  batch,  doubling  the  quantities  of  all 
materials  used.  The  cement  board  should  also  be  increased  to  10 
feet  x  12  feet,  as  shown  under  "  Tools."  In  this  case  the  mixing 
is  in  the  middle  of  the  board,  each  pair  of  men  mixing  exactly  as 
if  for  a  two-bag  batch,  except  that  the  concrete  is  shovelled  into  one 
big  mass  each  time  it  is  turned  back  on  to  the  centre  of  the  board. 
When  more  than  four  men  are  available,  the  rest  may  place  the 
concrete,  make  new  runs,  load  wheelbarrows,  etc.,  taking  the  con- 
crete away  from  the  board  as  fast  as  it  is  mixed.  In  this  case 
another  small  concrete  board  should  be  placed  next  to  the  big 
"  board,"  so  that  in  the  last  turning  the  batch  can  be  shovelled  over 
on  to  the  small  board  for  placing,  making  room  on  the  big  board  to 
mix  the  next  batch.  The  small  platform  need  be  only  just  big 
enough  to  hold  the  pile  of  mixed  concrete. 


TABLE  IV. 

SHOWING  THE  QUANTITIES  OF  MATERIALS  AND  THE  RESULTING  AMOUNT  OF 
CONCRETE  FOR  TWO-BAG  BATCH. 


PROPOR- 

TIONS BY 

TWO-BAG  BATCH. 

PARTS. 

• 

KIND  OP 
CONCRETE 
MIXTURE. 

13 
> 

Materials. 

Size  of  Measuring 
Boxes.     Inside 
Measurements. 

ss  . 

pi 

O 

O  m  « 

o 

*i 

°TJ 

1 

°-5J 

.ss^ 

0> 

§ 

V  > 

(_, 

<u  > 

fli        ^5 

I 

1 

a 

3 

CO 

0 

1 

c  g 

1 

1 

l| 

r^ 

Bags. 

Cu.  Ft. 

Cu.  Ft. 

Cu.   Ft. 

Gallons. 

1:2:4  Concrete 

i 

2 

4 

2 

3i 

7^ 

8^ 

2'   X   2' 

2'  X4' 

10 

XnJ* 

xny 

1:3:6  Concrete 

i 

3 

6 

2 

5f 

ni 

12 

2'    X3' 

3'X4' 

'31 

MIXING    CONCRETE    BY    MACHINE 

Machine  mixers  are  more  efficient  and  economical  than  hand 
labor  and  are  used  exclusively  on  all  large  jobs. 

In  machine  mixing,  the  making  and  placing  of  concrete  is 
divided  into  the  following  operations: 

[52] 


How  to  Mix  and  Place  Concrete 


1.  Transportation  of  the  raw  materials  to  the  stock  piles  or  bins. 

2.  Transportation  from  the  stock  piles  or  bins  to  the  mixer. 

3.  Proportioning,  mixing,  and  discharge  of  the  batch  into  buckets, 
cars,  or  other  vehicles. 

4.  Transportation  from  the  mixer  to  the  work. 

5.  Dumping,  spreading,  and  ramming. 

TABLE  V. 

SHOWING  THE  QUANTITIES  OF  MATERIALS  AND  THE  RESULTING  AMOUNT  or 
CONCRETE  FOR  TWO-BAG  BATCH  USING  NATURAL  MIXTURE  OF  BANK  SAND 
AND  GRAVEL. 


KIND  OF  CONCRETE 

MIXTURE. 

PROPOR- 
TION BY 
PARTS. 

TWO-BAG  BATCH  FOR  NATURAL  MIXTURE  OF 
BANK  SAND  AND  GRAVEL. 

Cement. 

11 

_x 
fe 

Materials. 

o 

c    . 

Size  of  Measur- 
ing Boxes. 

10 

Cement. 

Natural  Mix- 
ture of  Sand 
and  Gravel. 

Mixture  of 
Sand  and 
Gravel. 

1:2:4  Concrete  

I 

i 

4 
6 

Bags. 
2 
2 

Cu.  Ft. 

Cu.  Ft. 

12 

2'  X4'  X  ni" 
3'  X4'  X  iij" 

1:3:6  Concrete.. 

The  plant  required  depends  upon  the  size  of  the  job.  Boats, 
cars,  cableways,  conveyors,  derricks,  hoists,  and  other  appliances 
are  frequently  employed  for  transportation  purposes. 

Types  of  Mixing  Machines. — The  following  types  of  mixers  are 
in  general  use : 

a.  Tilting  mixtures. 

b.  Non-tilting  mixtures. 


i.  Batch  mixers 


(  a.  Hand  proportioning  of  ingredients. 
2.    Continuous  mixers.  4  .  °  ,. 

(  0.  Machine  proportioning  of  ingredients. 


3.  Gravity  mixers. . .  . 


a.  Trough  form  with  deflectors. 
6.  Hopper  form. 


i.  In  the  batch  mixers,  a  charge  of  cement,  sand,  aggregate,  and 
water  is  put  into  the  machine,  which  mixes  and  discharges  the 
batch  before  taking  in  another  charge. 

In  tilting  machines  the  concrete  is  discharged  by  raising  one 
end  of  the  drum  and  causing  the  mixture  to  flow  out  by  gravity. 

[53] 


Handbook  for  Cement  and  Concrete  Users 

In  non-tilting  mixers,  steel  deflectors  are  provided  in  the  drums, 
which  plough  through  and  pick  up  the  batch  as  the  drum  revolves. 
To  discharge  the  batch,  a  chute  is  provided.  When  this  chute  is 
tilted  so  that  one  end  projects  into  the  mixer,  the  material  picked 
up  by  the  deflectors  drops  back  on  to  the  chute  and  runs  out. 

The  special  features  of  the  batch  mixer  are  as  follows. 

1.  It  is  suitable  for  either  a  constant  delivery  of  large  quantities 
of  concrete,  or  for  small  quantities  at  irregular  intervals.     It  is, 
therefore,  the  only  type  fit  for  light  work  such  as  reinforced  concrete. 

2.  The   exact   proportions   specified   for  the   concrete   can  be 
assured  with  the  greatest  accuracy. 

3.  The  engineer  can  at  any  time  check  the  proportions  being  used. 


FIG.  9. — Concrete  Mixer  with  Automatic  Measuring  Devices.    (English  Type.) 

4.  The  amount  of  water  can  be  measured  exactly. 

5.  The  amount  of  mixing  given  to  the  concrete  is  under  the 
control  of  the  engineer,  and  by  specifying  a  definite  number  of 
revolutions  of  the  drum,  or  a  definite  time,  a  perfect  mixing  can  be 
assured. 

6.  A  preliminary  dry  mixing  can  be  given,  if  desired,  by  the 
machine.     . 

7.  The  different  materials  may  be  fed  to  the  mixing  apparatus 
separately.     There  is  therefore  no  necessity  for  hand  mixing  before 


54] 


How  to  Mix  and  Place  Concrete 

2.  Continuous  mixers  are  those  in  which  the  cement,  sand,  and 
stone  are  fed  to  the  charging  hopper  in  a  continuous  stream,  while 
the  mixed  concrete  is  discharged  in  another  continuous  stream. 

In  one  form  of  continuous  mixer  the  cement,  sand,  and  stone 
properly  proportioned  are  shovelled  directly  into  the  mixing  drum. 
In  the  other  form,  these  materials  are  dumped  into  separate  charg- 
ing hoppers  and  are  automatically  fed  into  the  mixing  drum  in 
any  relative  proportions  desired,  the  proportioning  being  accom- 
plished by  the  machine. 

Special  features  of  the  continuous  mixer. 

1.  It  is  of  use  chiefly  where  large  quantities  of  concrete  have  to 
be  delivered  without  intermission,  as  in  the  construction  of  sea  and 
dock  walls,  foundations,  etc.     It  is  not  suitable  where  only  small 
quantities  of  concrete  are  required  at  irregular  intervals,  as  in  the 
case  of  block-making  or  reinforced  concrete-work. 

2.  No  method  of  continuous  measuring  is  capable  of  the  same 
accuracy,  for  all  the  materials  concerned,  as  is  measuring  in  boxes 
or  skips. 

3.  It  is  impossible  for  the  engineer  to  exercise  the  necessary 
supervision  over  the  proportions  of  the  ingredients  used. 

4.  The  amount  of  water  in  the  concrete  will  depend  somewhat 
on  the  rate  of  running  of  the  machine,  and  cannot  be  accurately 
measured. 

5.  The  amount  of  mixing  given  to  the  concrete  is  not  under  the 
control  of  the  engineer,  but  is  fixed  chiefly  by  the  makers  of  the 
machine. 

6.  The  materials  cannot  be  satisfactorily  mixed  together  dry 
by  the  mixer  before  being  wetted,  although  the  attempt  to  do  this 
has  been  made  by  delivering  the  water  at  some  distance  from  the 
feed  opening. 

7.  All  the  materials  must  be  fed  into  the  mixer  simultaneously, 
since  there  is  a  continuous  movement  from  end  to  end,  and  if  fed 
separately  they  would  travel  separately  along  the  machine.     This 
means  that  a  preliminary  dry  mixing  by  hand  is  necessary  before 
feeding  into  the  machine. 

3.  Gravity  mixers  are  constructed  in  two  general  forms.  The  first 
form  is  a  trough  whose  bottom  and  sides  are  provided  with  pegs 
or  other  deflectors  which  give  the  material  a  zig-zag  motion  as  it 

[55] 


Handbook  for  Cement  and  Concrete  Users 

flows  along.  The  second  form  consists  of  a  series  of  hoppers,  set 
one  above  the  other,  so  that  the  batch  is  spilled  from  one  into  the 
next  and  is  thus  mixed. 

With  a  good  mixer  the  output  depends  upon  the  methods  of 


FIG.  10. — Trump  Automatic  Measuring  Arrangement. 

conveying  the  materials.  On  a  well  organized  job,  a  batch  mixer 
will  average  about  300  batches  in  ten  hours. 

On  large  jobs  with  labor  at  $2.00  per  day,  the  labor  cost  of 
putting  concrete  in  place  is  about  50  cents  per  cu.  yd.  When 
mixed  by  machine  and  deposited  by  hand,  this  cost  will  run  from 
75  cents  to  90  cents  per  cu.  yd. 

Precautions  in  Mixing. — In  mixing  concrete  by  machinery  the 
important  points  to  be  observed  are: 

i.  That  the  specified  proportions  of  the  ingredients  are  fed  into 
the  mixer  at  all  times. 

[56] 


How  to  Mix  and  Place  Concrete 

4 

2.  That  the  quantity  of  water  is  uniform  and  of  proper  amount 
to  produce  the  desired  consistency. 

3.  That    the    ingredients    are    thoroughly    incorporated   before 
leaving  the  mixer. 

/?0/>/>er 


\          L^ 


FIG.   ii. — Typical    Arrangement    of    Concrete    Mixing    Plant.      (Atlas    Portland 
Cement  Co.) 

4.  That  the  entire  contents  of  the  mixer  are  taken  out  at  each 
emptying. 

5.  When  the  mixer  is  stopped  it  should  be  flushed  with  water 
and  no  concrete  partially  set  or  otherwise  should  be  permitted  to 
remain  in  it. 

is?] 


Handbook  for  Cement  and  Concrete  Users 


6.  The  mixer  should  be  located  as  near  the  work  as  possible. 

7.  The  concrete  should  have  a  low  fall  when  leaving  the  mixer, 
not  giving  the  ingredients  an  opportunity  to  separate. 

8.  If  transported  the  concrete  must  be  carried  in  water-tight 
cars  or  barrows. 

9.  As  soon  as  placed  the  concrete  should  be  well  compacted,  all 
corners  being  thoroughly  filled. 

10.  The  forms  must  be  firm,  unyielding,  have  the  closest  possible 
joints  and  smoothed  on  the  inside. 

1 1.  A  richer  concrete  should  be  deposited  near  all  exposed  surfaces. 

12.  The  work  should  be  supervised  by  a  competent  inspector. 

PLACING  THE  CONCRETE 

How  Placed.* — After  the  concrete  is  properly  mixed  it  should  be 
placed  at  once.  Concrete  may  be  handled  and  placed  in  any  way, 
best  suited  to  the  nature  of  the  work,  provided  the 
materials  do  not  separate  in  placing.  Hand- 
mixed  concrete  may  be  properly  placed  by  shovel- 
ling off  the  concrete  board  directly  into  the  work, 
by  shovelling  into  wheelbarrows,  wheeling  to  place 
and  dumping,  by  shovelling  down  an  inclined 
chute,  or  by  shovelling  into  buckets  and  hoisting 
into  place.  Concrete  should  be  deposited  in 
layers  about  6  inched  thick  unless  otherwise 
specified. 

Consistency. — There  are  three  kinds  of  mix- 
tures used  in  general  concrete  work  as  follows : 

i.    Very  Wet 
Mixture.  —  Con- 
crete wet  enough 
to  be  mushy  and 
run  off  a  shovel 
when   handling. 
Used    for   rein- 
forced work,  thin  walls,  or  other  thin  sections,  etc. ;  no  ramming 
necessary. 

2.  Medium  Mixture. — Concrete  just   wet   enough  to  make  it 

*  See  foot  note  page  47. 

[58] 


FIG.  12. — Gravity  Mixer  for  Lining  Tunnel. 


How  to  Mix  and  Place  Concrete 


jelly-like.  Used  for  some  reinforced  work,  also  foundations,  floors, 
etc.  Ramming  with  tamper  or  treading  with  feet  necessary  to 
remove  air-bubbles  and  fill  voids.  In  concrete  of  a  medium  con- 
sistency, a  man  would  sink  ankle-deep  if  he  were  to  step  onto  the 
top  of  the  pile. 

3.  Dry  Mixture. — Concrete  like  damp  earth:  used  for  founda- 
tions, etc.,  where  it  is  important  to  have  the  concrete  set  up  as 
quickly  as  possible.  This  must  be  spread  out  in  a  4-inch  to  6-inch 


I 


FIG.  13. — Spading  Fine  Material  Adjacent  to  Form. 

layer  in  placing  and  thoroughly  tamped  until  the  water  comes  to  the 
surface. 

Spading. — Concrete  of  any  of  the  three  degrees  of  consistency 
mentioned  above  should  be  carefully  "spaded"  next  to  the  form 
where  the  finished  concrete  will  be  exposed  to  view.  "Spading" 
consists  of  running  a  spade  or  flattened  shovel  down  against  the 
face  of  the  form  and  working  up  and  down.  This  action  causes  the 
stone  or  gravel  to  be  pushed  back  slightly  from  the  form,  and  allows 
the  cement  grout  to  flow  against  the  face  of  the  form  and  fill  any  voids 

[59] 


Handbook  for  Cement  and  Concrete  Users 

that  might  be  there,  thus  making  the  face  of  the  work  present  an 
even,  homogeneous  appearance.  Where  the  narrowness  of  the 
concrete  section,  such  as  in  a  6-inch  silo  wall,  prevents  the  use  of  a 
spade,  a  i-inch-by-4-inch  board,  sharpened  to  chisel  edge  on  the 
end,  will  do  as  well.  Only  sharpen  on  one  side  and  place  the  flat 
side  against  the  form  as  shown  in  illustration.  In  the  case  of  a  dry 
mixture,  "spading"  must  be  done  with  greatest  care  by  experienced 
hands  to  get  uniform  results,  but  with  a  medium  or  wet  mixture  it 
is  very  easy  to  obtain  first-class  work;  indeed,  with  a  wet  mixture 


^Support  for 

\BeH-Co 

rse  fvrrr* 

1 

i 

\ 

i 

\ 

1 

r\ 

1 

A 

1 

*\ 

1 

^ 

V 

^ 

FIG.  14. — Enclosing  Building  with  Canvas  Curtains  to  Protect  the  Concrete. 

spading  is  required  only  as  an  added  precaution  against  the  poss- 
ibility of  voids  in  the  face  of  the  work,  and  is  really  necessary  in  few 
cases. 

Cleaning  the  Concrete  Board.— When  the  day's  work  is  done, 
carefully  clean  all  the  tools,  especially  the  concrete  board.  Remove 
with  a  shovel  all  the  loose  cement,  sand,  and  stone.  Then  scrub  the 
board  with  a  broom  and  water.  If  this  is  not  done,  small  particles 
of  stone  are  glued  to  the  board  by  the  cement,  and  render  shovelling 
the  next  day  most  difficult. 

Protection  of  Concrete  after  Placing. — Green  concrete  should 
not  be  exposed  to  the  sun  until  after  it  has  been  allowed  to  set  for 


How  to  Mix  and  Place  Concrete 

five  or  six  days.  Each  day  during  that  period  the  concrete  should 
be  wet  down  by  sprinkling  water  on  it,  both  in  the  morning  and 
afternoon.  This  is  done  so  that  the  concrete  on  the  outside  will 
not  dry  out  much  faster  than  the  concrete  in  the  centre  of  the  mass, 
and  should  be  carried  out  carefully,  especially  during  the  hot  summer 
months.  Old  canvas,  sheeting,  burlap,  etc.,  placed  so  as  to  hang 
an  inch  or  so  away  from  the  face  of  the  concrete  will  do  very  well 
as  a  protection.  Wet  this  as  well  as  the  concrete.  Often  the 
concrete  forms  can  be  left  in  place  a  week  or  ten  days;  this  protects 


FIG.  15. — Method  of  Depositing  Concrete  by  Chutes. 

the  concrete  during  the  setting-up  period  and  the  above  precautions 
are  then  unnecessary. 

Placing  Concrete  in  Freezing  Weather. — When  concrete  is  to 
be  placed  in  freezing  weather,  one  or  more  of  the  following  methods 
should  be  employed  to  protect  it  from  injury: 

1.  Lowering  the  freezing-point  of  the  mixing- water. 

2.  Heating  the  sand,  stone,  and  mixing- water. 

3.  Covering  and  housing  the  work. 

Common  salt  is  most  frequently  employed  for  the  purpose  of 
lowering  the  point  at  which  the  water  will  freeze.  The  rule  is  to 
add  salt  in  the  proportion  of  i  per  cent  of  the  weight  of  the  water 
for  each  degree  F.,  below  32°.  In  no  case,  however,  is  it  good 
practice  to  add  more  than  10  per  cent  of  salt. 

Sand  and  stones  are  heated  either  in  portable  heaters  or  in  bins. 

[61] 


Handbook  for  Cement  and  Concrete  Users 


When  bins  are  employed,  steam  pipes  are  used  to  thaw  out  the 
materials. 

Methods  of  covering  concrete  to  protect  it  from  light  frosts 
include  the  use  of  sacking,  shavings,  straw,  and  manure.  In  cold 
climates,  frame  buildings  that  completely  house  in  the  construction 
are  frequently  erected.  Such  buildings  are  heated  and  the  tem- 
perature kept  well  above  the  freezing-point. 

Placing  Concrete  Under  Water. — Mixed  concrete  if  emptied 
loose  and  allowed  to  sink  through  water  is 
destroyed;  the  cement  paste  is  washed  away 
and  the  sand  and  stone  settle  on  to  the  bottom 
more  or  less  segregated  and  practically  without 
cementing  value. 

To  overcome  these  difficulties,  the  follow- 
ing  methods  are  employed  for  depositing  con- 
crete under  water: 
i.  Depositing  in  j  a.  Bottom  dumping. 

closed  buckets  (  b.  Revolving  buckets. 
•-•-X     2.  Depositing  in  (  a.  Bottom  dumping  bags. 

bags (  Z>.  Bags  to  be  left  in  the  work. 

3.  Depositing  through  a  tremie. 

4.  Grouting  submerged  stone. 

Buckets  for  depositing  concrete  under  water 
are  provided  with  covers,  so  that  the  water 
cannot  flow  in  and  wash  out  the  cement  as 
the  material  is  being  lowered.  Bottom  dump- 
ing buckets  also  possess  an  unlocking  device  to 
open  the  bottom  doors  and  allow  the  concrete 
to  pass  out.  Revolving  buckets  are  turned 
upside  down  before  emptying. 

Two  methods  of  depositing  concrete  in  bags 
are  available  to  the  engineer.  In  the  first 
method  a  bag  of  heavy  tight-woven  material 
is  filled  with  concrete  and  emptied  at  the  bot- 
•;-;*:•; •*.-;*.>-.*.  torn,  the  bag  serving  like  the  buckets  as  a 

'  ^Concrete  f&SS&S-fSK?  r 

means  of  conveyance. 
FIG.    1 6.  —  Tremie         In   the   second  method  bags  of  paper  or 

Tube    for    Depositing   .  .  .          ,       ,_, 

Concrete  underwater!  loose-woven   gunny-sack    are  employed.     The 

[62] 


How  to  Mix  and  Place  Concrete 

bags  are  filled  with  concrete  and  are  left  in  the  work,  the  idea 
being  that  the  paper  will  soften  or  the  cement  ooze  out  through 
the  openings  in  the  cloth  sufficiently  to  bond  the  separate  bagfuls 
into  a  solid  mass. 

A  tremie  consists  of  a  tube  of  wood  or  sheet  metal,  which  reaches 
from  above  the  surface  to  the  bottom  of  the  water.  It  is  operated 
by  filling  the  tube  with  concrete  and  keeping  it  full  by  successive 
additions,  while  allowing  the  concrete  to  flow  out  gradually  at  the 
bottom  by  slightly  raising  the  tube  to  provide  the  necessary  opening. 

Masses  of  gravel,  broken  or  rubble  stone  deposited  under  water 
may  be  cemented  into  what  is  virtually  a  solid  concrete  by  charging 
the  interstices  with  grout  forced  through  pipes  from  the  surface. 
The  grout  employed  is  a  i  :  i  mixture  of  Portland  cement  and  sand, 
with  sufficient  water  to  form  a  thick  paste.  This  is  readily  forced 
through  2  in.  pipes  into  depths  of  50  ft.  and  over. 

In  heavy  subaqueous  operations  concrete  is  also  placed  by 
constructing  a  coffer  dam  around  the  site,  pumping  out  the  water, 
and  working  in  the  dry  or  by  placing  large  specially  prepared  blocks 
by  means  of  derricks,  the  setting  being  done  by  divers.  A  new 
method  has  recently  come  into  use  for  building  subaqueous  concrete 
walls,  by  means  of  pontoons  constructed  on  shore,  floated  into  place 
and  sunk  by  means  of  ballast. 


[63] 


CHAPTER  VIII 

FORMS  FOR  CONCRETE  CONSTRUCTION 

Kinds  of  Forms. — Pressure  of  Concrete  on  Forms. — Dressing  and  Lubrication  of 
Forms. — Design  of  Forms. — Removing  Forms. — Cost  of  Forms. 

THE  design  and  construction  of  forms  are  among  the  most 
difficult  of  the  problems  imposed  upon  the  worker  in  concrete. 

Forms  should  be  stiff,  strong,  and  economical  in  labor  and 
materials.  They  should  be  built  with  a  view  to  economy  in  taking 
down  rather  than  to  cheapness  in  erecting  or  in  first  cost.  Roughly 
built  forms  which  cannot  be  removed  without  being  ripped  to 
pieces  are  always  expensive. 

Kinds  of  Forms. — The  principal  kinds  of  forms  in  general  use 
are  as  follows: 

1.  Simple  braced  forms. 

2.  Wired  and  bolted  forms  for  walls. 

3.  Forms  made  of  studding  and  matched  boards. 

4.  Panel  forms. 

5.  Column  forms  and  braces. 

6.  Forms  for  beams  and  slabs. 

7.  Arch  centres. 

8.  Special,  collapsible  facing  forms  and  templets. 

Forms  are  most  commonly  constructed  of  wood,  which  must  be 
planed  and  oiled  to  present  a  smooth  surface,  since  the  concrete 
takes  the  impress  of  any  irregularity  that  presents  itself.  Stiff, 
close-grained  woods  are  the  best,  such  as  white  pine,  yellow  pine, 
spruce,  Oregon  pine,  or  redwood.  Hemlock  should  not  be  employed, 
as  it  is  rough,  splintery,  and  weak.  Oak  is  hard  to  nail,  expensive 
and  imprints  grain  marks  on  the  concrete  even  when  the  form  is  well 
oiled. 

Forms  should  be  constructed  in  such  a  way  as  to  avoid  the  use 
of  nails  whenever  possible.  Braces  are  seldom  less  than  i  in. 
thick  and  it  takes  hard  driving  to  get  spikes  through  them.  When- 

[64] 


Forms  for  Concrete  Construction 

ever  possible,  blocks  or  wedges  held  in  place  by  thin  nails,  should 
be  substituted  for  the  large  spikes  so  often  employed. 

Lagging  and  panel  strips  are  made  of  i  1/4  to  2  inch  stuff,  short 
struts  and  braces  of  2  x  4  inch  timber,  while  long  struts  range  from 
4  x  4  to  8  x  8  inch  sectional  area. 

Simple  braced  forms  are  used  for  foundations,  retaining  walls, 
and  ordinary  construction.  They  consist  of  from  i  to  i  1/2  inch 
boards,  which  are  supported  by  2  x  4  inch  studs,  set  about  2  feet 
apart.  The  studs  are  also  braced  with  2x4  inch  diagonals.  The 
diagonal  braces  are  held  in  position  by  posts  driven  into  the  ground. 


FIG.  17. — Simple  Forms  for  Cellar  Walls.    This  type  is  faulty  in  that  the  braces 
are  nailed  to  the  sides. 

"As  a  rule  it  is  best  to  drive  a  line  of  posts  and  to  lay  against  them 
a  heavy  timber  or  thick  plank.  This  provides  a  stiff  support  against 
which  braces  may  be  placed  at  any  point  when  needed.  At  any 
sign  of  giving  way  in  the  forms,  intermediate  braces  may  be  quickly 
introduced  without  the  delay  consequent  upon  driving  new  posts." 
"Bracing  is  not  good  practice  for  the  holding  of  wall  forms  in 
place."  Failures  of  such  forms  are  frequently  caused  by  the  giving 
way  of  the  posts  due  to  the  yielding  of  earth.  Earth  is  a  poor 
material  to  depend  upon  for  holding  forms  rigid,  and  bracing  is 
only  excusable  when  the  form  can  be  secured  from  but  one  side 
and  that  usually  the  outside.  In  all  narrow  forms,  the  studding 
on  opposite  sides  should  be  tied  together  by  bolts  or  wires. 
5  [65] 


Handbook  for  Cement  and  Concrete  Users 

In  all  braced  forms,  the  posts  against  which  the  ends  of  the 
diagonals  rest  should  be  driven  deep.  "They  should  also  be 
driven  as  nearly  vertical  as  possible.  The  usual  way  is  to  drive 
them  on  a  slant,"  but  experience  has  shown  that  vertical  posts  are 
the  stiff er,  especially  when  the  ground  is  poor.  "The  top  soil  is 
seldom  able  to  carry  much  of  a  load,"  hence  the  brace  should  be 
driven  deep  in  order  that  it  may  obtain  sufficient  anchorage. 

Wired  and  Bolted  Forms. — Forms,  when  used  on  both  sides  of  a 
narrow  wall,  should  be  tied  together  by  wires  or  bolts.  The  wire 


FIG.  1 8. — Showing  Method  of  Wiring  Forms. 

is  preferably  passed  twice  through  the  forms,  the  ends  twisted 
together  and  any  surplus  cut  off  with  nippers,  while  the  wire  is 
tightened  by  twisting,  the  two  strands  together  inside  of  the  forms, 
a  stick  being  employed  for  the  purpose.  Before  it  is  drawn  up,  a 
wooden  spacer  of  length  equal  to  the  required  width  of  the  wall  is 
placed  beside  the  wire,  where  it  is  left  until  the  concrete  reaches 
that  height,  after  which  it  is  removed. 

Wired  forms  are  much  more  secure  than  those  which  are  merely 
braced.  They  possess,  however,  the  following  objectionable 
features : 

[66] 


Forms  for  Concrete  Construction 

1.  The  ends  of  the  wires  are  exposed  when  the  forms  have  been 
removed. 

2.  The  wooden  spacers  are  sometimes  left  in  the  concrete. 

3.  The  wire  gives  a  little,  as  the  concrete  is  tamped,  causing 
the  form  to  bulge.     There  is  no  practicable  way  of  taking  up  this 
give. 

To  overcome  these  objections  bolts  are  frequently  employed 
instead  of  twisted  wire.     Wooden  spacers  can  be  removed  as  soon 


FIG.  19.— The  Dietrich  Plank  Holders. 

as  the  bolts  are  tightened,  while  the  give  can  be  taken  up  by 
tightening  the  nuts  on  the  bolts.  Such  bolts  are  withdrawn 
after  the  forms  have  been  removed  and  the  holds  are  filled 
with  cement  paste  mixed  with  some  waterproofing  compound. 
This  method  is,  however,  objectionable  where  an  impervious 
seal  is  required,  as  the  oil  placed  on  the  bolts  to  permit  of 
their  removal  prevents  a  watertight  bond  between  the  post  and 
the  body  of  the  wall. 

To  avoid  this  difficulty  a  number  of  arrangements  are  in  use 
whereby  two  short  bolts  are  connected  to  wire  loops  in  the  body  of 
the  wall.  The  wire  loops  remain  in  the  wall,  so  that  the  main 
portion  is  solid  and  impervious,  while  the  shallow  holes,  left  on  each 
side  when  the  bolts  are  withdrawn,  are  filled  with  cement  paste  to 
preserve  its  sightliness.  Mr.  Ernest  McCullough  uses  a  device 
consisting  of  two  thumb-nuts  connected  by  wire  loops  into  which 
the  threaded  ends  of  the  bolts  are  placed.  They  are  then  screwed 
up  until  the  head  of  the  bolt  bears  against  the  face  of  the  form, 
which  is  protected  by  a  washer.  See  Fig.  18. 


Handbook  for  Cement  and  Concrete  Users 

Forms  Made  of  Studding  and  Matched  Boards. — Two  designs 
are  in  use: 

i.  Where  the  boards  are  nailed  to  the  inside  of  the  studding  and 
the  form  erected  as  a  unit. 


FlG.  20. — Forms  for  Reinforced  Concrete  Retaining  Wall. 


FIG.  21. — The  Farrel  Plank  Holder. 

2.  Where  the  studding  is  erected  and  braced,  and  the  boards 
set  one  at  a  time  without  nailing.  This  design  is  much  more  con- 
venient for  pouring,  as  the  concrete  is  only  the  width  of  a  board 
below  the  top  of  the  form,  which  is  built  up  as  the  work  proceeds. 

[68] 


Forms  for  Concrete  Construction 

Good  inspection,  however,  is  required  to  insure  proper  construction 
and  bracing  where  form  work  and  placing  of  concrete  are  going  on 
simultaneously. 

Panel  Forms  are  an  amplification  of  the  "  board-by-board " 
method,  several  boards  being  fastened  together  and  erected  as  a 
unit,  or  united  by  nails  and  braces  into  box-like  forms.  The  follow- 
ing types  are  in  general  use : 

a.  The  Ransome  panel  consists  of  a  number  of  boards,  which 
are  fastened  together  by  cleats  on  the  back  and  held  in  position  by 
slotted  frames  or  studs.  The  studs  are  set  opposite  each  other  and 
are  bolted  through  at  top  and  bottom.  Spacers  are  also  set  in 
position  to  keep  the  frames  the  proper  distance  apart.  As  soon  as 
the  panel  has  been  filled  with  concrete,  "the  lower  bolt  is  withdrawn, 


FIG.  22. — Panel  Method  of  Framing  for  Wall  Construction. 

and  the  slotted  frames  raised  to  a  height  as  great  as  may  be  obtained 
when  the  upper  bolt  reaches  the  bottom  of  the  slot.  The  lower 
bolt  is  then  passed  through  the  upper  part  of  the  slot  with  a  new 
spacer  to  preserve  the  interval,  and  work  is  recommenced." 

b.  Framed  panels  consist  of  i-inch  boards  braced  with  2x4 
inch  wales  and  uprights,  the  panels  being  about  12  feet  long  by  4 
feet  in  height.  For  any  wall  at  least  two  lines  of  panels  are  em- 
ployed, and  for  high  walls,  three  sets  should  be  available  to  avoid 
delays  to  the  work.  The  panels  are  braced  by  bolts  and  spacers. 
Bolts  are  placed  at  the  top  of  the  forms,  and  are  provided  with  large 
washers  which  also  bear  against  the  bottom  of  the  superimposed 
forms  and  hold  them  in  position  when  placed. 

Column  Forms. — For  columns  it  is  customary  to  provide  a 
vertical  trough  and  to  brace  the  forms  by  horizontal  frames  made  of 

[69] 


Handbook  for  Cement  and  Concrete  Users 

2x4  inch  stuff.     These  frames  are  of  several  types  of  which  the 
following  are  in  common  use : 

a.  Timber  frames  which  consist  of  four  strips,  one  on  each  side 
of  the  column.     These  are  held  together  by  means  of  lugs  and 
hardwood  wedges. 

b.  Bolted  frames  which  consist  of  two  strips  on  opposite  sides  of 
the  column  form.     These  are  tied  together  by  bolts.     The  strips 


FIG.  23.— Movable  Wall  Forms. 

exert  pressure  on  opposite  sides  of  the  form,  while  the  other  two 
sides  are  secured  by  hardwood  wedges  between  the  bolts  and  the 
form.  These  are  placed  as  close  as  possible  to  the  ends  of  the  bolts. 

c.  Clamped  frames,  in  which  metal  clamps  are  used  to  hold  the 
form  together,  as  the  Hennebique  Column  Form  Clamp. 

In  some  cases  the  sides  of  the  form  are  made  up  of  narrow 
strips.  This  is  to  facilitate  the  reduction  in  size  of  the  columns 
from  floor  to  floor.  In  warm  weather  there  is  no  need  of  having 
more  column  forms  than  one  complete  set  for  one  story.  Each  of 
the  narrow  strips  represents  the  reduction  in  diameter  of  the  column 
from  one  story  to  the  next. 

In  removing  forms  the  column  moulds  are  taken  down 
first.  It  is  therefore  necessary  to  so  design  the  details  about  the 


Forms  for  Concrete  Construction 

tops  of  the  forms  as  to  permit  of  their  removal  without  in  any 
way  disturbing  the  beam  and  girder  moulds. 

Beam  and  Slab  Forms. — Beam  forms  are  horizontal  troughs 
made  of  i  or  i  1/4  inch  lumber.  The  bottom  piece  rests  on  two 
2x4  inch  stringers  which  in  turn  are  supported  by  4  x  4  inch  caps 
resting  on  posts.  The  side  pieces  are  braced  with  2x4  inch 
horizontal  strips  at  top  and  bottom,  and  by  vertical  and  inclined 


FIG.  24. — Column  Form  and  Method  of  Bracing. 

webbing  of  the  same  size.  For  shallow  beams,  a  lighter  construc- 
tion can  be  employed. 

When  the  floor  slabs  and  their  supporting  girders  are  built 
monolithic,  a  2  x  4  inch  strip  is  nailed  along  the  outside  of  the 
beam  forms  to  carry  the  flooring  for  the  slabs.  Cross  bracing  is 
also  wedged  between  ihe  girder  forms  in  order  to  stiffen  the  con- 
struction and  to  assist  in  carrying  the  loads  to  the  parts  under  the 
girders  which  support  the  entire  load.  The  middle  of  the  floor 
slab  form  is  further  supported  by  a  2  x  4  inch  piece  resting  on  the 
cross  bracing. 

In  removing  beam  and  girder  forms,  the  posts  should  be  taken 
from  only  one  girder  at  a  time,  and  as  soon  as  the  form  for  this 
has  been  removed,  the  posts  should  be  immediately  replaced 


Handbook  for  Cement  and  Concrete  Users 

and  wedged  up.  By  this  procedure,  danger  of  failure  of  concrete 
through  poor  workmanship  is  much  diminished,  as  a  defective 
member  is  supported  by  the  members  on  either  side  of  it  until  the 
defect  can  be  remedied. 

"An  essential  thing  about  arch  centres  is  that  they  must  be 
perfectly  rigid  so  that  the  arch  will  not  be  stressed  in  the  slightest 


Sicr/at  TMMOV&I  Guwtna 

FlG.  25. — Typical  Forms  for  Reinforced  Concrete  Factory  Floors. 

degree  before  the  concrete  attains  a  perfect  set,  and  yet  they  must 
be  so  placed  that  their  removal  will  be  accomplished  without 
injuring  the  surface  of  the  concrete  and  without  straining  the  arch. 
All  centres  must  be  dropped  away  from  the  arch  readily.  Salvage 
of  material  is  an  important  item,  but  as  a  rule  the  salvage  is  higher 
with  arch  centres  than  with  forms  for  buildings.  Much  of  the 

[72] 


Forms  for  Concrete  Construction 

material  consists  of  posts  and  sway  braces,  and  these  require  but 
little  cutting." 

Special  Forms. — Pressed  steel  forms  are  used  to  a  limited  extent 
in  concrete  column,  girder,  and  slab  construction  and  their  use  is 
likely  to  increase  in  the  near  future  on  account  of  the  rapid  rise  in 
the  price  of  lumber.  The  chief  difficulties  in  the  use  of  such  forms 
are  their  liability  to  leakage,  tendency  to  rust  and  possible  injury 
by  dents  in  removing. 

Centering. — Collapsible  centres  which  consist  of  a  steel  or 
timber  shell  supported  by  interior  bracing  and  so  constructed  that 
the  shell  can  be  readily  removed  and  placed  in  a  new  position  are 
extensively  used  for  pipes  and  conduits.  Several  forms  are  built, 
of  which  the  following  are  examples : 

Half  round  steel  centres  on  circular  conduits. 

Full  round  steel  centres  for  monolithic  construction. 

Box  centres  for  concrete  culvert  construction. 

Shaft  lining  and  tunnel  centering. 

Centres  for  cut  and  cover  conduit  construction. 

A  facing  form  is  a  steel  plate  which  is  placed  on  edge  at  the 
proper  distance  back  from  the  lagging  and  the  space  between  filled 
with  facing  mortar.  The  form  is  finally  lifted  up  and  the 
backing  and  facing  thoroughly  bonded  by  tamping  them  .together. 
It  is  used  when  a  mortar  finish  is  required,  of  greater  thickness 
than  can  be  obtained  by  spading  the  coarser  aggregate  back  from 
the  surface  of  the  forms. 

Pressure  of  Concrete  on  Forms. — The  forms  for  concrete  must 
be  strong  enough  to  withstand  the  pressure  of  the  "soupy  "  mass, 
and  girder  forms  must  be  stiff  enough  so  that  their  deflection  as 
the  weight  increases  will  not  cause  partial  rupture  of  the  concrete 
or  sagging  of  the  beam. 

Experiments  have  shown  that  forms  designed  on  the  assump- 
tion that  the  pressure  produced  by  wet  concrete  is  equivalent  to 
that  of  a  fluid  weighing  80  pounds  per  cubic  foot  are  reasonably  safe. 

"In  ordinary  walls  where  the  concrete  is  placed  in  layers,  compu- 
tation is  not  usually  necessary,  since  general  experience  has  shown 
that  maximum  spacing  for  i-inch  boards  is  2  feet,  for  1-1/2  inch 
plank  is  4  feet,  and  for  2 -inch  plank  is  5  feet.  Studding  generally 
varies  from  2x4  inches  to  4  x  6  inches,  according  to  the  character 

[73] 


Handbook  for  Cement  and  Concrete  Users 


of  the  work  and  the  distance  between  the  horizontal  braces  or 
walling." 

Dressing  and  Lubrication  of  Forms. — Dressed  lumber  should 
be  employed  for  all  exposed  surfaces  in  order  to  give  a  smooth 
finish.  Dressed  timber  also  permits  tighter  joint  construction,  and 
facilitates  the  removal  and  cleaning  of  the  forms. 

All  forms  for  concrete  require  a  coating  of  some  lubricant  to 
prevent  the  concrete  from  adhering  to  the  wood  with  which  it  comes 

TABLE    VI. 

SHOWING  THE  PRESSURE  ON  FORMS  PRODUCED  BY  CONCRETE  AT 
VARIOUS  DEPTHS. 


Depth  in  Feet. 

i 

2 

4 

6 

8 

12 

16 

20 

24 

Pressure  on  Vertical  strip,  i 
foot  wide  in  pounds  .  . 

40 

160 

640 

I4.4O 

2t;6o 

^760 

10240 

16000 

23040 

Pressure  on  i  square  foot 
in  pounds 

80 

1  60 

•32O 

A8O 

640 

060 

1280 

1600 

IO2O 

in  contact.  Crude  oil  is  generally  employed  for  the  purpose,  but 
any  grease  that  will  spread  evenly  and  fill  the  pores  of  the  wood  will 
answer  equally  well.  The  use  of  lubricants  reduces  the  cost  of 
removing  the  forms  and  also  gives  a  smoother  finish  to  the  concrete. 
Forms  should  not  be  removed  until  the  concrete  has  attained 
sufficient  strength  to  carry  the  load.  Wet  concrete  sets  more 
slowly  than  dry  mixtures,  and  concrete  is  slower  setting  in  cold 
weather  than  it  is  when  the  weather  is  warm. 

For  walls,  the  forms  should  be  left  up  from  i  to  5  days;  for 
slabs,  from  6  days  to  2  weeks;  for  beams  and  girders,  from  2  to  4 
weeks;  and  for  large-sized  arches,  from  i  to  3  months. 

Design  of  Forms. — The  following  formula  is  employed  in 
designing  forms  and  is  recommended  by  Sanford  E.  Thompson: 

Assume 

1.  Weight  of  concrete,  including  reinforcement,   154  Ibs.   per 
cu.  ft. 

2.  Live  load — 75  Ibs.  per  sq.  ft.  upon  slab;    50  Ibs.  per  sq.  ft. 
in  figuring  beam  and  girder  forms;  and  struts. 

3.  For  allowable  compression  in  struts  use  600  to  1,200  Ibs.  per 

[74] 


Forms  for  Concrete  Construction 

sq.  in.,  varying  with  the  ratio  of  the  size  of  the  strut  to  its  length. 
If  timber  beams  are  calculated  for  strength,  use  750  Ibs.  per  sq.  in., 
extreme  transverse  fibre  stress. 

4.  Compute  plank  joists  and  timber  beams  by  the  following 
formula,  allowing  a  maximum  deflection  of  1/8  inch: 


384    El 
and 


(x) 


in  which 

d  =  Greatest  deflection  in  inches. 

W  =  Total  load  on  plank  or  joist  in  pounds. 

I  =  Distance  between  supports  in  inches. 

E  =  Modulus  of  elasticity  of  lumber  used. 

/  =  Moment  of  inertia  of  cross-section  of  plank  or  joist. 

b  =  Breadth  of  lumber. 

h  =  Depth  of  lumber. 

For  spruce  lumber  and  other  woods  commonly  used  in  form 
construction,  E  may  be  assumed  as  1,300,000  pounds  per  square 
inch. 

Formula  (i)  may  be  solved  for  /,  from  which  the  size  of  joist 
required  may  be  readily  estimated  from  formula  (2). 

Time  to  Move  Forms  after  Placing.*  —  The  proper  time  for 
removing  forms  depends  upon  the  character  of  the  construction. 
The  following  rules  are  applicable  to  ordinary  practice: 

Walls  in  mass  work:  one  to  three  days,  or  until  the  concrete 
will  bear  pressure  of  the  thumb  without  indentation. 

Thin  walls:   in  summer,  two  days;   in  cold  weather,  five  days. 

Slabs  up  to  6  feet  span:  in  summer,  six  days;  in  cold  weather, 
two  weeks. 

Beams  and  girders  and  long  span  slabs:  in  summer,  ten  days  or 
two  weeks;  in  cold  weather,  three  weeks  to  one  month.  If  shores 
are  left  without  disturbing  them,  the  time  of  removal  of  the  sheeting 
in  summer  may  be  reduced  to  one  week. 

*  By  Sanford  E.  Thomson. 
[75] 


Handbook  for  Cement  and  Concrete  Users 

Column  forms:  in  summer,  two  days;  in  cold  weather,  four 
days,  provided  girders  are  shored  to  prevent  appreciable  weight 
reaching  columns. 

Conduits:  two  or  three  days,  provided  there  is  not  a  heavy  fill 
upon  them. 

Arches:  of  small  size,  one  week;  for  large  arches  with  heavy 
dead  load,  one  month. 

All  of  these  times  are,  of  course,  simply  approximate,  the  exact 
time  varying  with  the  temperature  and  moisture  of  the  air,  and  the 
character  of  the  construction.  Even  in  summer  during  a  damp, 
cloudy  period,  wall  forms  sometimes  cannot  be  removed  inside  of 
five  days  with  other  members  in  proportion.  Occasionally,  too, 
batches  of  concrete  will  set  abnormally  slow  either  because  of  slow- 
setting  cement  or  impurities  in  the  sand,  and  the  foreman  and 
inspector  must  watch  very  carefully  to  see  that  the  forms  are  not 
removed  too  soon.  Trial  with  a  pick  may  assist  in  reaching  a 
decision. 

Beams  and  arches  of  long  spans  must  be  supported  for  a  longer 
time  than  short  spans  because  the  dead  load  is  proportionately 
large,  and  therefore  the  compression  in  the  concrete  is  large  even 
before  the  live  load  comes  upon  it. 

Cost  of  Forms. — The  cost  of  form  work  per  cubic  yard  of  con- 
crete depends  largely  on  the  thickness  of  the  walls.  With  very 
thin  walls  the  cost  for  forms  is  comparatively  high,  and  for  such 
work  a  method  of  estimating  which  is  based  on  the  surface  area 
should  be  employed. 

There  are  three  methods  of  estimating  the  cost  of  form 
work: 

1.  In  cents  per  cubic  yard  of  concrete. 

2.  In  cents  per  square  foot  of  surface  area  of  concrete. 

3.  In  dollars  per  1,000  ft.  B.  M.  of  lumber  used. 

The  cost  of  form  work  is  made  up.  of  the  cost  of  the  lumber  and 
the  labor  of  framing,  erection,  and  removal  of  the  forms.  Lumber 
costs  from  $20  to  $30  per  1,000  ft.  B.  M.,  and  if  used  three  times, 
the  cost  of  the  lumber  will  range  from  2  to  3  cents  per  square  foot 
of  surface  area  of  concrete. 

Ordinary  forms  for  walls  and  mass  work  can  be  erected  and 


Forms  for  Concrete  Construction 

taken  down  for  $10  per  M.  For  beams  and  arches  the  labor 
cost  is  much  higher.  Such  work  cannot  be  even  approximately 
estimated  from  any  rule  of  thumb,  but  must  be  carefully  computed 
from  the  detailed  plans  of  the  structure;  taking  account  of  the  size 
of  the  job,  the  special  difficulties  to  be  overcome,  and  the  prevailing 
cost  of  common  and  skilled  labor  in  the  locality. 


[77] 


SECTION  II 
CONCRETE   ARCHITECTURE 


CHAPTER  IX 

THE  ARCHITECTURAL  AND  ARTISTIC    POSSIBILITIES 

OF    CONCRETE 

A  New  Style  of  Architecture. — For  a  century  or  more  architects 
have  been  vainly  trying  to  create  a  new  style  of  architecture;  back 
and  forth  they  have  vacillated,  but  never  forward.  They  have 
tried  every  possible  combination  of  the  ancient  masterpieces  but 
without  results;  and  it  seems  that  again,  as  in  the  fable  of  old,  the 
hidden  treasure  was  not  in  foreign  lands  but  right  at  our  own  door,— 
beneath  our  very  feet.  It  is  a  recognized  principle  of  architecture 
that  the  material  of  which  a  structure  or  monument  is  made  is 
(after  the  idea  or  need  that  called  it  into  existence)  the  main  factor 
in  determining  the  form,  color,  and  structure  of  the  monument. 
This  being  true,  it  is  likely  that  a  material,  having  so  many  char- 
acteristics that  no  other  material  has,  is  certain  to  introduce  many 
new  features  into  a  structure  and  finally  create  a  new  style  of 
architecture;  and  this  is  especially  probable  because  designs  hitherto 
attainable  in  other  material  only  at  great  expense,  can  be  obtained 
so  cheaply  in  concrete. 

It  is  so  easy  to  obtain  very  high  ornamentation  in  concrete  that 
it  is  necessary  for  the  artist  to  exercise  self  denial  in  refraining  from 
unmeaning  display  for  the  sake  of  show.  The  popular  notion  that 
architecture  is  the  heaping  of  pretty  things  onto  a  structure  to  hide 
its  construction  is  wrong.  True  art  is  always  the  result  of  a  clear 
and  forceful  expression  of  the  idea  and  use  of  the  structure.  Ex- 
pression in  art  must  be  obtained  by  making  some  parts  plainer 
than  others,  thus  bringing  out  the  richness  or  elegance  of  the  main 
idea.  Make  your  structure  look  like  what  it  is, — concrete;  solid, 
strong,  substantial,  beautiful.  The  ornamentation  chosen  taste- 

[78] 


Architectural  Possibilities  of  Concrete 

fully  to  accord  with  the  idea  expressed  and  with  the  natural  sur- 
roundings, construct  with  a  feeling  of  modesty,  dignity,  simplicity, 
and  repose,  and  you  will  have  a  design  alive  with  purpose  that  will 
live  through  the  ages. 

Mr.  R.  VanDeerlin,  Chief  Engineer,  Hennebique  Construction 
Company,  says: 

"Concrete,  with  the  aid  of  steel,  is  adaptable  to  almost  every 
kind  of  structure,  not  only  economically  but  architecturally.  Un- 
fortunately it  has  been  handicapped  by  the  attempt  to  force  it  to 
imitate  other  materials.  This  probably  results  from  its  plasticity 
and  reluctance  to  depart  from  well  recognized  methods  of  architect- 
ural design.  Being  generally  composed  of  stone  for  an  aggregate, 
it  somewhat  naturally  suggests  that  the  same  line  of  design  would 
be  appropriate  for  concrete  as  has  become  the  recognized  standard 
for  stone.  Such,  however,  is  not  the  case,  as  there  is  a  material 
difference  in  the  general  appearance.  After  the  temptation  to 
imitate  is  overcome  the  plasticity  of  concrete  makes  it  not  only  an 
excellent  building  material  but  also  an  architectural  one  as  well. 

"The  most  striking  examples  of  architectural  beauty  are  noted 
for  their  simplicity  and  freedom  from  confusing  details  and  effects 
that  distract  the  attention  from  the  ,keynote  of  the  design.  Previous 
to  this  century,  the  limitations  of  building  operations  have  made  it 
necessary  to  have  the  size  of  the  units  of  construction  small  in  order 
'  to  keep  the  cost  within  bounds.  This  gave  definite  construction 
joints  which  were  accentuated  and  developed  along  certain  lines  to 
create  certain  impressions.  Now  that  concrete  is  available,  it  is 
no  longer  necessary  to  have  these  lines  or  joints  and  they  can  be 
eliminated  entirely  or  used  only  where  they  are  really  an  architectural 
benefit.  Simplicity  in  concrete  design  is  to  be  desired  also  from  an 
economical  standpoint,  because  one  of  the  most  expensive  items  in 
concrete  construction  is  the  form  work.  The  cost  can  be  trebled 
easily  if  the  forms  are  complicated. 

"  The  future  of  concrete  treated  architecturally  lies  in  a  development 
on  surfaces  and  not  lines.  Who,  for  instance,  would  prefer  a  concrete 
bridge,  built  to  represent  one  of  cut  stone  to  one  where  the  con- 
crete is  honestly  shown  on  pleasing  surfaces,  free  from  the  lines 
which  are  supposed  to  represent  the  joints  of  the  stones,  and  only 
showing  the  lines  which  are  there  for  purely  architectural  reasons. 

[79] 


Handbook  for  Cement  and  Concrete  Users 

If  it  were  possible  to  economically  eliminate  the  joint  lines  from  the 
stone  bridge,  it  is  very  probable  that  no  one  would  ever  have  at- 
tempted to  use  similar  artificial  lines  for  effect.  Compare  a  con- 
crete tower  treated  as  a  monolith  with  one  built  to  imitate  stone. 
The  plain  surface  is  far  more  pleasing  than  the  other.  Compare 
also  the  many  pleasing  concrete-surfaced  houses  with  those  con- 
structed with  the  rough  concrete  blocks. 

"  When  the  problem  of  arranging  the  structural  parts  of  a  building 
is  considered,  there  is  no  material  that  so  readily  lends  itself  to  the 


FIG.  26. — Section  of  Reinforced  Concrete  Cathedral  at  Poti,  Russia.    Showing 
Architectural  Possibilities  on  Important  Edifices.     (Hennebique.) 

required  adjustment  as  reinforced  concrete,  both  economically  and 
effectively.  If  a  perfectly  flat  ceiling  is  desired,  the  structural  floor 
can  be  designed  in  the  mushroom  system  or  constructed  with  terra- 
cotta and  concrete.  The  slight  additional  expense  of  these  two 
methods  over  an  ordinary  slab-and-beam  construction  is  less  than 
the  cost  of  an  expanded  metal  lath  and  plaster  ceiling,  as  plaster 
can  be  very  easily  applied  directly  to  the  surface  of  either.  If  the 
rooms  are  small  the  doubly  armed  panel  allows  them  to  be  freed 
from  projecting  beams  as  the  beams  can  be  placed  over  the  par- 


Architectural  Possibilities  of  Concrete 

titions.  This  system  is  also  adaptable  to  large  rooms,  where 
paneled  ceilings  are  desired." 

Concrete  block  architecture  and  handsome  stucco  effects,  both 
of  which  are  treated  in  succeeding  chapters,  have  come  into  extensive 
use,  the  former  now  emerging  from  a  period  of  doubt  and  suspicion 
following  the  influx  into  the  market  of  poorly  made  material,  a 
question  which  will  be  discussed  later  on. 

The  preparation  and  artistic  treatment  of  concrete  surfaces 
have  done  a  great  deal  in  developing  the  architectural  possibilities 
of  concrete,  and  much  credit  is  due  to  the  pioneers  in  bringing  out 
the  many  beautiful  surface  finishes.  It  is  only  necessary  to  go  to 
sections  like  Long  Beach  on  the  Long  Island  southern  coast  and 
see  the  varied  styles  of  beautiful  concrete  residences,  to  realize  that 
a  new  architecture  has  been  born,  which,  owing  to  its  economy  and 
fireproofness,  as  well  as  beauty,  will  supplant  the  classics  of  bygone 
days. 


81] 


CHAPTER  X 

CONCRETE  RESIDENCES 

The  Use  of  Concrete  for  Residences. — Best  Method  of  Obtaining  Architectural 
Effects. — Stucco  and  Reinforced  Concrete  for  Residences. — The  Edison  Poured 
Concrete  House:  Cost  of  Different  Types  of  Residences  Compared. 

As  stated  in  the  previous  chapter,  the  architectural  treatment  of 
concrete,  until  recent  years,  was  limited  to  an  attempted  imitation 
of  stone  masonry,  which  tended  to  cheapen  its  appearance  and  to 
destroy  its  character.  As  an  imitation  of  stone,  concrete  is  not  an 
artistic  success.  There  is  a  sameness  to  its  appearance,  an  air  of 
sombreness,  an  absence  of  light  and  color  that  destroys  its  architec- 
tural value. 

Within  the  present  century  the  secret  of  the  artistic  use  of  con- 
crete has  been  revealed,  and  with  this  discovery  has  come  such 
recognition  by  architects  and  owners  alike,  that  concrete  has  already 
taken  its  place  within  the  front  ranks  of  building  materials,  and  its 
growing  use  is  indicative  of  a  future  whose  possibilities  and  benefits 
to  humanity  are  transcendent. 

The  secret  of  the  successful  use  of  concrete  for  architectural 
purposes  consists  in  such  treatment  of  its  surface  as  will  serve  to 
bring  out  its  true  character  and  to  reveal  its  hidden  beauties.  These 
methods  are  in  part  described  in  the  chapter  on  "  Artistic  Treatment 
of  Concrete  Surfaces,"  and  consist  in  the  use  of  carefully  chosen 
aggregates;  tooled,  scrubbed,  etched,  or  pebble-finished  surfaces, 
stuccos  of  varied  tints  and  textures;  the  artistic  use  of  half -timber 
framing,  of  columns,  cornices,  pediments  and  balusters  to  lend 
variety;  and  an  attractive  shingled  or  tiled  roof  to  form  an  effective 
covering. 

Concrete  is  now  employed  in  the  construction  of  all  classes  of 
residences,  such  as  bungalows,  costing  from  $500  to  $1,000;  cot- 
tages, from  $1,500  to  $2,500;  moderate  priced  houses  from  $3,000 
to  $5,000;  and  palaces  in  which  the  cost  of  construction  requires 
five,  six,  or  even  seven  figures  for  its  expression. 

[82] 


Concrete  Residences 

Kinds  of  Concrete  Residences. — In  these  different  classes  of 
residences,  Portland  cement  mortar  and  concrete  are  used  in  one  or 
more  of  the  following  forms: 

1.  Hollow  concrete  blocks. 

2.  Monolithic  concrete. 

3.  Stucco. 

Concrete  Block  Residences. — Hollow  concrete  blocks  have 
outnumbered  all  other  forms  in  which  concrete  is  employed  in 
residential  construction,  owing  to  their  cheapness  and  ease  of 
construction.  Their  description  and  manufacture  will  be  found  in 
Chapter  XIII. 

Early  manufacturers  of  concrete  blocks  were  unfortunate  in  try  ing 
to  mould  the  surfaces  in  imitation  of  quarry-faced  stone,  and  the 
effect  of  their  efforts  was  to  produce  a  structure  without  beauty  or 
variety.  "A  rock-faced  stone  is  the  result  of  an  actual  treatment 
of  the  stone  with  tools,  and  no  two  rock-faced  stones  are  alike. 
There  is  variety  to  the  surface."  But  with  concrete  blocks  the 
variety  is  lacking.  "  Even  when  several  rock-faced  moulds  are  used 
and  the  blocks  are  made  of  different  patterns,  it  generally  happens 
that  several  having  exactly  the  same  face  from  the  same  mould  come 
together,  and  that  is  exceedingly  noticeable." 

Surface  Finishes  for  Block  Residences. — The  best  architectural 
effects  in  concrete  block  residences  are  produced  with  the  following 
surfaces : 

1.  Perfectly  plain  surfaces. 

2.  Roughened,  or  pebble-finished  surfaces. 

3.  Surfaces  produced  by  casting  in  sand  moulds. 

4.  Surfaces  of  pure  white  color  or  delicately  tinted. 

Some  of  the  finest,  as  well  as  the  least  expensive  residences  are 
now  constructed  of  plain  blocks,  the  facades  being  relieved  by 
columns  and  cornices  in  moulded  concrete,  the  roofs  covered  with 
ornamental  tiles  of  red  or  other  warm  tones,  and  the  piazzas  having 
concrete  rails  and  balusters  of  appropriate  design. 

Roughened  surfaces  are  produced  by  scrubbing,  etching  with 
acid,  and  treating  with  wire  brushes,  the  object  being  to  destroy 
the  film  of  surface  cement  and  to  expose  the  aggregate.  By  the 
use  of  granite  chips,  colored  gravel,  crushed  marble,  or  coarse  white 
sand,  various  effects  are  obtained,  and  the  architect  who  possesses 

[83] 


Handbook  for  Cement  and  Concrete  Users 

originality  and  a  knowledge  of  the  possibilities  of  his  material,  can 
produce  striking  and  artistic  effects  at  a  very  moderate  cost.  These 
will  be  treated  further  in  Chapter  XII. 

Casting  in  sand  moulds  is  generally  confined  to  mouldings,  balus- 
ters, columns,  and  other  ornamental'  features.  "  Sand  moulding  gives, 
perhaps,  the  handsomest  ornament  of  any  kind  of  moulding  process, 
the  surface  texture  and  detail  of  the  block  being  especially  fine." — 
(Gillette.) 

Surface  tints  are  best  produced  by  the  use  of  colored  gravels. 
Pure  white  surfaces  are  obtained  by  using  facing  mortars  composed 
of  white  limestone  or  crushed  white  marble  and  white  Portland 
cement.  Such  mortars  can  also  be  tinted  with  delicate  colors  by 
the  use  of  appropriate  pigments. 

Monolithic  Residences. — Houses  having  solid  walls  of  monolithic 
concrete  are  best  treated  by  making  the  surfaces  of  the  walls  un- 
broken without  attempting  to  imitate  masonry  or  joints  in  stones. 

The  following  methods  of  surface  treatment,  which  are  more 
fully  explained  in  Chapter  XII,  are  well  adapted  to  such  construc- 
tion: 

1.  Spading  the  concrete  so  as  to  cause  the  grout  to  flush  to  the 
surface  of  the  forms.     This  prevents  the  exposure  of  the  aggregate 
and  any  defects  can  be  remedied  by  trowelling  and  grouting  after 
the  forms  have  been  removed. 

2.  Roughening  the  surface    by  scrubbing,  etching  with    acid, 
tooling  with  bushhammers  or  pneumatic  hammers,  etc. 

3.  Use  of  colored  aggregate  or  of  granite  chips,  white  quartz 
pebbles,  or  other  special  materials  which  are  exposed  by  scrubbing 
or  tooling. 

4.  Surfacing  with  mortar  or  stucco. 

5.  Tinting. 

Stucco  Residences. — Any  mortar  employed  as  an  exterior  sur- 
facing for  walls  is  called  stucco.  Cement  stucco  is  extensively  used 
both  for  renovating  old  buildings  and  improving  their  appearance 
and  in  new  construction.  The  methods  of  application  are  fully 
described  in  the  succeeding  chapter. 

The  classes  of  residences  in  which  a  stucco  finish  is  of  advan- 
tage are  as  follows : 

[84] 


Concrete  Residences 

1.  Old  houses  composed  of  wood,  stone,  brick,  concrete,  or 
other  materials  in  which  the  surface  is  worn  or  decayed. 

2.  New  houses  composed  of  wood,  stone,  brick,  concrete,  or 
other  materials,  in  which  the  surface  is  left  rough  or  unfinished. 

3.  Houses  having  hollow  walls  of  expanded  metal,  terra  cotta 
or  concrete  tile,  or  other  fabric,  and  covered  inside  and  out  with 
mortar  or  stucco. 

Portland  cement  stucco  is  easily  applied  to  any  material  such  as 
wood,  brick,  stone,  etc.,  by  covering  the  surface  with  a  metal  fabric 
over  furrowing  strips  to  serve  as  an  anchorage  for  the  mortar. 
Wooden  lathing  can  also  be  employed  for  this  purpose,  and  in  the 
case  of  frame  houses  spaces  can  be  left  between  the  boards  to  serve 
as  a  key. 

Stucco  is  composed  of:  (a)  cement  and  sand;  (b)  white  Port- 
land cement  and  either  white  sand,  crushed  white  quartz,  ground 
marble,  or  ground  white  limestone;  (c)  cement  and  granite  chips; 
(d)  cement  and  colored  gravel;  (e)  cement  and  pebbles,  etc.  White 
stucco  is  also  readily  tinted  with  delicate  colors  by  the  admixture 
of  colored  pigments. 

Concrete  for  residences,  whether  in  the  form  of  hollow  blocks, 
or  monolithic  walls,  requires  waterproofing.  Basement  walls 
should  be  surrounded  by  a  bituminous  shield,  or  a  waterproofing 
compound  should  be  mixed  with  the  cement  employed  in  the 
blocks  or  walls  since  it  is  desirable  to  render  the  entire  exterior 
surface  as  impervious  to  moisture  as  possible.  In  old  leaky 
buildings,  a  coat  of  damp-resisting  paint  on  the  exterior  surface 
will  be  effective. 

Reinforced  Concrete,  which  is  extensively  employed  in  factory 
construction,  is  coming  into  use  for  dwellings  in  order  to  permit  of 
lighter  walls  and  partitions.  The  reinforcement  is  chiefly  in  the 
form  of  expanded  metal  or  other  fabric  which  is  nailed  to  the 
studding  on  both  sides,  thus  forming  a  support  for  the  plastering. 
In  pretentious  houses,  rods  are  also  employed  to  distribute  the 
loads  over  foundation  areas  and  to  prevent  temperature  cracks. 
Concrete  beams  are  employed  only  to  a  limited  extent  in  residences, 
as  the  interior  joists  are  almost  invariably  of  wood,  as  are  also  the 
floors,  purlins,  rafters,  and  roof  trusses.  While  this  is  the  present 
practice,  it  is,  however,  no  criterion  of  the  state  of  the  art  a  few 

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Handbook  for  Cement  and  Concrete  Users 

years  hence,  when  it  is  probable  that  the  "all-concrete"  house  will 
have  ceased  to  be  a  novelty. 

Special  Architectural  Features. — At  present  concrete  is  used 
to  a  limited  extent  for  roofing  purposes  in  the  form  of  slabs  and 
tiles,  although  red  terra  cotta  tiles  and  wooden  shingles  are  chiefly 
employed  for.  pitched  roofs  and  tin  plates  or  gravel  for  flat  roofs. 

Concrete  houses,  especially  those  of  a  suburban  character,  are 
frequently  built  with  a  prominent  roof  of  steep  pitch,  large  piazzas, 
bay-windows  and  the  English  half-timbered  construction  above 
the  lower  stories.  This  consists  of  wooden  strips  around  the 
windows  forming  the  trim  and  radiating  from  the  upper  windows  to 
the  roof.  These  strips  are  also  used  as  mouldings  and  serve  to 
bring  out  the  lines  of  the  gables,  adding  much  to  the  appearance 
of  the  dwelling. 

Other  decorative  features  of  concrete  houses  are  the  columns, 
rails,  and  balusters  of  the  piazzas  which  may  be  of  wood  or  concrete, 
preferably  the  latter;  the  free  use  of  dormer  windows  in  the  roof, 
chimneys  of  concrete  blocks  or  of  monolithic  construction  in  har- 
mony with  the  general  design,  horizontal  mouldings  between  the 
stones,  prominent  lintels,  and  massive  cornices. 

The  use  of  concrete  in  interiors  is  at  present  confined  chiefly  to 
stairs,  panels,  fireplaces,  and  bath  rooms.  Stairs  are  reinforced 
with  bars  and  surfaced  with  a  white  mortar  or  are  tinted  to  harm- 
onize with  the  woodwork  of  the  halls;  fireplaces  are  built  of  concrete 
bricks  moulded  and  tinted  to  any  desired  shade;  while  concrete  slabs 
and  tiling  or  mosaic  laid  in  white  Portland  cement  mortar  is  used 
for  mosaic  floors,  wainscoating,  bath-rooms,  and  fireplaces,  taking 
the  place  of  Keene's  cement  which  it  excels  in  strength  and  dur- 
ability. 

Edison  Cast  Concrete  House. — Thomas  A.  Edison,  the  electrical 
wizard,  has  experimented  for  several  years  in  developing  a  sub- 
stantial and  cheap  house  of  cement,  and  has  published  the  following 
particulars  of  his  work : 

"I  believe  a  cement  house  can  be  built  by  machinery  in  lots 
of  100  or  more  at  one  location  for  a  price  which  will  be  so  low  that 
it  can  be  purchased  or  rented  by  families  whose  total  income  is 
not  more  than  $550  per  annum.  My  experiments  have  proven 
that  it  is  possible  to  cast  a  house  complete  in  six  hours  by  pouring 

[86] 


Concrete  Residences 

a  very  wet  mixture  of  gravel,  sand,  and  cement  into  iron  moulds 
having  the  form  of  a  house,  and  after  the  removal  of  the  forms  or 
moulds,  leave  standing  a  complete  house  with  a  fine  surface,  plain 
or  ornamental,  all  in  one  solid  piece,  including  the  cellar,  partitions, 
floors,  roof,  stairs,  mantels,  veranda — in  fact  everything  except  the 
windows  and  doors,  which  are  of  wood  and  the  only  parts  of  the 
house  that  are  combustible. 

"The  house  is  to  be  heated  by  boiler  and  radiators  in  the 
usual  manner,  the  plumbing  to  be  •  open  and  jointed  by  electric 
welding. 

"The  experimental  house  has  the  partitions  arranged  to  give, 
besides  the  cellar,  two  rooms  on  first  story  (one  to  be  used  as  a  living 
room  and  the  other  for  a  kitchen);  the  second  story  to  have  two 
rooms  and  bath;  the  roof  story  to  have  two  rooms.  When  large 
numbers  of  houses  are  made,  the  partitions  can  be  changed  to 
make  more  rooms.  Once  the  house  is  cast,  however,  no  changes 
can  ever  be  made — nothing  but  dynamite  could  be  used  to  remove 
a  partition  without  great  expense. 

"With  a  few  simple  additions  to  the  iron  forms,  a  great  many 
variations  in  the  type  of  the  houses  can  be  made.  For  instance, 
by  adding  or  subtracting  iron  sections,  the  house  can  be  made 
smaller  and  cheaper.  By  adding  sections,  the  number  of  stories 
can  be  increased,  or  it  can  be  widened  or  lengthened.  By  a  few 
additional  forms,  the  whole  appearance  of  the  veranda  can  be 
changed.  A  contracting  company  having  the  smallest  unit  possible 
to  permit  of  cheap  and  rapid  production,  must  have  six  sets  of 
moulds  with  the  other  necessary  machinery.  From  these  iron 
sections  almost  any  variation  in  the  size,  appearance,  and  orna- 
mentation of  the  row  of  houses  can  be  made.  The  concrete  could 
be  tinted  with  any  kind  of  color,  but  the  general  type  would  be  the 
same.  The  units  might  be  divided  and  thereby  three  complete 
moulds  for  one  type  of  house  and  three  sets  for  an  entirely  different 
type,  would  be  secured. 

"This  scheme  of  constructing  houses  cheaply  and  in  quantities 
does  not  permit  of  the  building  of  one  house  at  a  time,  for  the 
reason  that  the  moulds  are  heavy.  The  machinery  necessary  to 
handle  the  materials  as  well  as  for  the  erection  of  the  iron  moulds, 
is  large  and  expensive, 

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Handbook  for  Cement  and  Concrete  Users 

"The  hardening  of  the  cement  requires  four  days.  While  one 
house  was  hardening  the  men  would  either  have  to  remain  idle  or 
be  laid  off  during  this  period,  and  this  would  not  be  practicable; 
whereas,  if  the  full  unit  of  a  minimum  of  six  sets  of  moulds,  and 
machinery  was  in  operation,  the  thirty-seven  men  necessary  could 
be  employed  continuously  erecting,  pouring,  and  removing  forms 
from  one  lot  to  another,  at  a  minimum  of  expense. 

"Houses  of  this  type,  I  believe,  can  be  built  for  $1,200  each, 
in  any  community  where  material  excavated  from  the  cellar  is  sand 
and  gravel,  so  it  can  be  used.  If  the  sand  and  gravel  must  be 
obtained  elsewhere,  the  cost  will  be  much  more.  A  change  in  the 
forms  can  be  made  so  that  a  house  can  be  built  that  will  look  just 
as  well,  but  smaller,  at  a  less  cost.  On  the  other  hand,  by  addition 
to  the  forms,  houses  costing  $2,000  or  $3,000  or  more  can  be  built. 

"To  give  a  rough  idea  of  the  cost,  I  estimate  that  six  sets  of  iron 
forms  for  the  house  I  am  to  build  will  cost  about  $25,000  per  house 
— a  total  cost  of  $150,000.  The  cranes,  traction  steam  shovel, 
conveying  and  hoisting  machinery,  I  estimate,  will  cost  $25,000 
additional,  making  a  total  investment  of  $175,000.  With  this 
machinery  twelve  (12)  houses  per  month  can  be  made  every  month 
in  the  year,  with  the  aid  of  one  foreman,  one  engineer,  and  thirty- 
five  (35)  laborers.  This  gives  one  hundred  and  forty-four  (144) 
houses  per  year  for  the  unit.  If  I  can  prove  this,  then  the  labor 
cost  per  house  will  not  exceed  $150  each. 

"If  we  allow  6  per  cent  interest  and  4  per  cent  for  breakage 
on  the  cost  of  the  forms,  and  6  per  cent  interest  with  15  per  cent 
depreciation  on  machinery,  the  yearly  expense  will  be  about  $20,000. 
Dividing  this  into  the  144  houses  built  in  the  year,  gives  approxi- 
mately $140  per  house,  for  cost  of  moulds  and  machinery.  220 
barrels  of  cement  will  be  mixed  with  the  sand  and  gravel  excavated 
from  the  cellar,  and  will  provide  sufficient  material  to  build  the 
house.  Allowing  $1.40  per  barrel  for  cement,  adds  a  further  sum 
of  $310.  The  reinforcing  steel  rods  cost  $125;  and  the  heating 
system  and  bath  $150.  These  items  total  $875.  This  leaves  a 
margin  between  that  sum  and  $1,200  of  $325  to  provide  for  doors, 
windows,  etc.,  painting,  and  the  correction  of  any  possible  defects. 

"If  the  houses  are  smaller  and  225  can  be  built  in  the  year  for 
the  same  investment  and  labor,  it  will,  from  the  above  data,  be 

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Concrete  Residences 

easy  to  approximate  the  cost  per  house;  the  same  is  true  with  larger 
size  houses. 

"These  houses  will  be  waterproof  and  dampproof.  The  roofs, 
after  the  forms  are  removed,  are  painted  with  a  paint  made  of 
cement  tinted  with  red  oxide  of  iron,  which  hardens  and  never 
deteriorates.  Cement  can  be  tinted  to  any  color  and  any  shade  of 
that  color,  and  the  inside  or  outside  can  be  painted,  and  is  per- 
manent. The  cost  of  the  paint  for  the  whole  house,  inside  and 
out,  including  roof,  will  be  very  small. 

"  Should  the  experiment  succeed,  I  will,  without  cost,  furnish 
all  plans,  give  full  license  to  reputable  building  corporations  without 
cost,  as  I  am  not  making  these  experiments  for  money. 

"I  think  the  age  of  concrete  has  started  and  I  believe  I  can 
prove  that  the  most  beautiful  houses  that  our  architects  can  conceive 
can  be  cast  in  one  operation  in  iron  forms  at  a  cost,  which  by  com- 
parison with  present  methods,  will  be  surprising.  Then  even  the 
poorest  man  among  us  will  be  enabled  to  own  a  home  of  his  own— 
a  home  that  will  last  for  centuries  with  no  cost  for  insurance  or 
repairs,  and  be  as  exchangeable  for  other  property  as  a  United 
States  Bond." 

The  following  table,  compiled  by  the  National  Fireproofing  Co., 
gives  a  good  idea  of  the  comparative  cost  of  various  classes  of 
residences. 

COMPARATIVE  COST  OF  VARIOUS  TYPES  OF  RESIDENCES. 

(A  $10,000  frame  residence  is  taken  as  a  unit.) 

Frame   construction,   all  wood $10,000 

Brick  outside  walls,  wooden  interior 11,000 

Stucco  or  expanded  metal,  wooden  interior 10,250 

Hollow  terra  cotta  blocks,  stuccoed,  wooden  interior 10,500 

Hollow  terra  cotta  blocks,  stuccoed,  fireproof  throughout,  except  roof.  12,000 

Hollow  terra  cotta  blacks  faced  with  brick,  fireproof  floors.     .     .     .  14,000 

Brick  walls,  fireproof  floors i5>ooo 

Houses  can  be  built  with  terra  cotta  blocks  for  walls  and  floors 
with  wooden  roofs  at  a  cost  of  twenty-two  cents  per  cubic  foot;  if 
built  with  wooden  floors  and  roof,  at  eighteen  cents  per  cubic  foot. 


[89] 


CHAPTER  XI 

MORTARS,  PLASTERS,  AND  STUCCOS,  AND  HOW  TO 

USE  THEM 

The  Art  of  Stuccoing.— Lime  Mortars  and  Plasters.— Interior  Plasters  and  Plastering. 
— Gypsum  Plasters. — Portland  Cement  Plasters  or  Stucco. — Exterior  Lathing  and 
Plastering. — Application  of  Stucco  to  Stone. — Stucco  on  Brick. — Stucco  on 
Concrete. — Quantities  of  Materials  for  Stucco. 

THE  art  of  using  mortars  is  as  old  as  civilization;  the  pyramids 
of  Egypt  contain  plaster  work  executed  at  least  four  thousand  years 
ago;  very  early  in  Greek  architecture  a  true  lime  stucco  of  thin 
white  composition  was  employed  as  a  ground  on  which  to  paint 
their  decorative  ornament;  the  Romans  were  familiar  not  only 
with  lime  and  plaster,  but  with  hydraulic  cement  as  well. 

There  is  every  reason  to  believe  that  originally  these  stuccoes 
were  intended  to  cover  up  and  protect  inferior  building  stone  and 
sunburned  straw  brick.  The  archaeology  of  stucco  would  tend 
to  show  that  from  an  artistic  standpoint  this  method  of  decoration 
was  a  development  of  the  wattled  buildings,  which  were  plastered 
with  clay  and  different  muds  hardened  by  being  baked  in  the  heat 
of  the  sun.  Therefore,  in  this  instance,  the  use  of  clay  plaster 
over  wattled  houses  was  to  protect  an  inferior  building  material. 

At  the  present  time,  mortars  and  plasters  are  among  the  most 
familiar  materials  employed  by  the  builder.  These  consist  of  three 
general  classes,  which,  however,  grade  into  each  other  when  mixed 
in  different  proportions : 

1.  Lime  plasters. 

2.  Gypsum  plasters. 

3.  Portland  cement  plasters  or  stucco. 

Lime  is  used  for  interior  plastering  where  the  walls  are  to  be 
papered;  gypsum  or  plaster  of  Paris,  where  a  white  or  hard  surface 
is  desired;  and  Portland  cement  mortar  for  exteriors  where  strength 
and  durability  are  required. 

Lime  Mortars  and  Plasters. — As  already  explained  in  Chapter 
II,  lime  is  produced  by  heating  a  pure  or  nearly  pure  limestone  in  a 


Mortars,  Plasters,  and  Stuccos 

kiln  to  such  a  temperature  as  will  drive  off  the  carbonic  acid  gas 
and  leave  calcium  oxide  or  " quick  lime."  When  water  is  added 
to  quick  lime  it  changes  from  a  lumpy  condition  to  a  soft,  im- 
palpable powder  known  as  "slaked  lime."  When  more  water  is 
added,  the  slaked  lime  becomes  a  paste,  and  this  paste  is  mixed 
with  sand  to  form  a  mortar. 

Mortar  for  plaster  work  is  usually  composed  of  slaked  lime, 
mixed  with  sand  and  hair.  The  sand  should  be  hard,  sharp,  gritty, 
and  free  from  all  organic  matter.  Pit  sand  is  generally  sharp  and 
angular  and  is  preferable  to  river  and  sea  sands,  which  are  more 
rounded  and  are  apt  to  contain  saline  particles  that  may  cause 
efflorescence. 

Hair  is  used  as  a  binding  medium  to  increase  the  cohesion  and 
tenacity.  Good  hair  should  be  long,  strong,  and  free  from  grease 
or  other  impurities.  Ox  hair  is  generally  used,  although  sometimes 
adulterated  with  the  short  hair  of  horses.  Substitutes  for  hair 
include  manila  fibre  and  sawdust. 

Interior  Plastering. — Lime  mortar,  when  used  as  a  plaster  for 
walls  and  ceilings,  is  placed  preferably  in  three  coats  on  wooden  or 
metal  laths.  On  brick  or  tile  walls,  and  in  residence  construction 
two  coats  are  often  considered  sufficient,  and  for  rough  plastering, 
one  coat.  Three-coat  work  makes  a  straight,  smooth,  strong,  and 
sanitary  surface  for  walls  and  ceilings  when  properly  executed. 
The  processes  employed  for  the  different  coats  are  as  follows: 

1.  Scratch  coat. 

2.  Brown  coat. 

3.  Finish. 

First  or  Scratch  Coat. — The  first  or  scratch  coat  should  be  from 
3/8  to  5/8  of  an  inch  thick,  composed  of  i  part  of  lime  paste  to  2 
of  sand,  and  i  bushel  of  hair  to  2  of  lime.  The  plaster  should  be 
stiff  enough  to  cling  and  hold  up  when  laid,  yet  sufficiently  soft  and 
plastic  to  go  through  the  interstices  between  the  laths,  leaving 
a  trowelful  partly  overlapping  the  previous  one,  the  one  binding  the 
other. 

Scratching  consists  in  scoring  the  surface  of  the  first  coat  to 
obtain  a  key  for  the  following  one.  It  is  done  with  a  wooden  or 
iron  scratch,  which  may  have  from  one  to  five  points.  The  first 
coat  should  be  allowed  to  stand  for  an  hour  or  two  so  as  to  allow 


Handbook  for  Cement  and  Concrete  Users 

the  stuff  to  become  firm,  after  which  the  surface  is  cross-scratched 
diagonally,  the  scores  being  about  11/4  inch  centre  to  centre. 
Scratching  with  a  single  point  is  more  easily  controlled  and  less 
likely  to  make  the  scores  too  deep  than  is  the  case  where  a  four-  or 
five-pointed  scratch  is  used.  It  requires,  however,  considerably 
more  time  for  the  operation.  Scratching  with  the  point  of  a  trowel 
should  not  be  permitted.  The  use  of  a  trowel  as  a  scratch  is 
detrimental  to  the  strength  of  the  mortar,  as  its  sharp  edge  cuts  the 
hair.  It  also  leaves  a  smooth  and  narrow  key,  which  presents 
no  means  of  attachment  for  the  second  coat. 

When  the  first  coat  is  applied  to  brick,  stone,  or  concrete  walls, 
the  superfluous  mortar  in  the  joints  should  be  raked  out  and  the 
walls  roughened  to  form  a  bond;  the  walls  should  also  be  well 
swept  and  thoroughly  wetted  to  prevent  the  absorption  of  water 
from  the  mortar. 

Second  or  Brown  Coat. — The  brown  coat  should  be  from  3/8 
to  5/8  of  an  inch  thick  and  should  contain  i  part  of  lime  to  3  of 
sand  and  i  bushel  of  hair  to  five  of  lime.  Before  the  second  coat  is 
applied,  the  scratch  coat  should  be  well  swept  to  clean  off  any 
dust  that  may  have  accumulated  and  a  damp  brush  passed  lightly 
over  the  surface  to  prevent  the  absorption  of  moisture  from  the 
second  layer.  The  object  of  the  second  or  brown  coat  is  to  form  a 
straight  surface  for  the  finishing  coat.  The  process  consists  of 
the  following  operations : 

a.  Plumbing  and  levelling  "screeds"  to  act  as  bearings  for  the 
floating  rule  and  running  mould. 

b.  Filling  in  the  spaces  between  the  screeds. 

c.  Scouring. 

d.  Keying  the  surface  for  the  finishing  coat. 

Screeds  are"  the  guides  on  the  margins  of  walls  and  ceilings 
between  which  the  plastering  is  placed.  They  consist  of  narrow 
strips  of  plaster,  which  are  leveled  in  the  case  of  a  ceiling,  or  tested 
by  plumb  line  in  the  case  of  a  wall.  Large  surfaces  on  walls  or 
ceilings  should  be  divided  into  bays  by  narrow  screeds  placed  from 
6  to  9  feet  apart.  This  affords  more  freedom  and  regularity  for 
filling  in  and  ruling  off  the  bays. 

Filling  in  consists  of  laying  the  intervening  spaces  between  the 
screeds  with  mortar,  and  then  ruling  the  surface  straight  and  flush 

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Mortars,  Plasters,  and  Stuccos 

with  the  screeds  by  means  of  a  floating  rule.  In  this  operation, 
two  men  are  required  for  each  bay.  These  work  the  rule  up  and 
down  with  a  cutting  motion,  keeping  it  in  a  slightly  angular  posi- 
tion, so  that  any  surplus  stuff  will  not  fall  on  the  man  below.  A  rule 
should  not  be  worked  on  either  of  its  face  edges,  as  by  so  doing  it 
becomes  round  and  uneven.  The  filling  in  and  ruling'  off  is  con- 
tinued until  all  the  walls  are  completed. 

Scouring. — This  consists  in  consolidating  the  surface  by  sprink- 
ling it  with  water  and  rubbing  it  vigorously  with  a  hand  float.  The 
work  should  be  done  as  soon  as  the  surface  is  firm  and  before  it 
becomes  dry.  The  operation  is  of  great  importance,  as  it  tends  to 
prevent  cracks  in  its  own  body  and  in  the  subsequent  or  finishing 
coat.  The  float  is  applied  with  a  rapid  circular  motion,  using  a 
little  fine  mortar  to  fill  up  any  small  holes  or  inequalities  that  may 
have  been  left  after  the  floating  rule.  The  floating  should  be 
scoured  twice,  or  for  best  work  three  times.  The  final  scouring 
should  be  continued  until  there  is  little  or  no  moisture  left  on  the 
surface.  From  three  to  five  hours  should  be  allowed  to  elapse 
between  the  first  and  second  scouring;  and  at  least  twelve  hours 
between  the  second  and  last. 

Keying. — This  consists  in  roughening  the  surface  by  means  of 
a  wire  brush  or  a  hand  float  with  the  point  of  a  nail  projecting  about 
1/8  inch  beyond  its  sole.  A  tool,  called  a  " devil"  is  also  employed 
for  this  purpose,  and  consists  of  a  small  float  with  four  nail  points 
projecting  from  the  sole. 

Third  or  Finishing  Coat. — The  application  of  the  final  coat 
consists  of  three  operations,  as  follows: 

a.  Laying. 

b.  Scouring. 

c.  Trowelling. 

The  material  employed  for  the  final  coat  is"  called  setting-stuff 
and  consists  of  lime  putty  and  washed,  fine,  sharp  sand,  in  the 
proportions  of  3  parts  of  sand  to  i  of  putty.  Lime  putty  may  be 
kept  for  an  indefinite  time  without  injury  if  protected  from  the 
atmosphere,  but  when  exposed  an  inert  crust  is  formed  by  the  action 
of  the  carbonic  acid  gas  which  it  absorbs  from  the  air. 

The  setting  stuff  is  laid  in  two  coats,  the  second  following  im- 
mediately upon  the  first.  The  laying  is  best  done  with  a  skimming 

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Handbook  for  Cement  and  Concrete  Users 

float,  which  leaves  the  face  of  the  first  coat  rougher  to  receive  the 
second  than  if  done  by  a  laying  trowel.  The  second  coat  should 
also  be  laid  with  a  skimming  float,  which  leaves  a  more  open  grain 
for  the  purpose  of  scouring. 

Scouring  the  Finishing  Coat. — This  consists  of  sprinkling  with 
water  and  rubbing  vigorously  to  consolidate,  harden,  and  render 
the  surface  of  a  uniform  texture  and  evenness.  The  work  should 
be  well  and  thoroughly  scoured,  twice  with  water  and  an  ordinary 
hand  float  and  finally  with  a  cross-grained  float,  which,  having  sharp 
square  edges,  cuts  off  all  inequalities  and  leaves  the  setting  with  a 
uniform  and  even  surface.  The  scouring  is  continued  until  a  dense, 
even  and  close-grained  surface  is  obtained  for  the  trowelling. 

Trowelling. — This  is  the  final  operation  and  follows  immediately 
after  the  scouring.  The  plasterer  sprinkles .  water  on  the  surface 
and  works  the  trowel  in  long  and  vigorous  strokes,  first  downwards 
and  upwards,  and  then  crossways  or  diagonally.  Water  is  applied 
with  a  brush,  and  the  operation  is  repeated,  using  the  water  more 
sparingly,  and  finishing  or  trowelling  off  with  an  up-and-down 
motion  which  should  leave  the  surface  free  from  "fat"  or  " gleet." 
The  finishing  coat  should  average  1/8  of  an  inch  in  thickness,  and 
should  not  be  less  than  1/6  nor  more  than  3/16  of  an  inch.  If  too 
thick,  it  is  liable  to  crack  and  flake;  and  if  too  thin,  to  peel.  Where 
extra  strength  is  desired,  the  first  coat  of  the  setting  should  contain 
a  little  white  hair,  which  does  not  show  through  the  last  coat. 

Colored  Finish. — A  beautiful  color  and  brilliant  finish  for  walls 
may  be  obtained  by  mixing  an  equal  quantity  of  sifted  marble  dust 
with  setting  stuff  and  using  this  as  a  final  coat.  Ordinary  finish  is 
greatly  improved  by  substituting  a  part  of  marble,  alabaster,  or 
gypsum  dust,  equal  in  bulk  to  half  the  sand  generally  used.  The 
marble  dust  should  be  as  coarse  as  the  sand.  Brick  dust  is  also 
used  for  coloring,  while  ground  glass,  when  added,  produces  a 
sparkling  surface.  Any  of  the  pigments  employed  in  coloring 
stucco  can  also  be  used  for  tinting  the  finishing  coat. 

Gypsum  Plasters — Gypsum  is  a  sulphate  of  lime,  and  when 
heated  so  as  to  drive  off  the  water  of  crystallization,  and  ground  to 
a  powder,  it  acquires  the  property  of  hardening  on  the  application 
of  water,  with  which  it  combines  in  the  proportion  of  about  4  parts 
of  gypsum  to  i  of  water  by  weight.  When  prepared  for  the  use  of 

[94] 


Mortars,  Plasters,  and  Stuccos 

the  plasterer,  gypsum  is  commonly  called  plaster  or  plaster  of  Paris. 
The  finest  gypsum  is  called  alabaster,  which  is  soft,  pure  in  color 
and  fragile,  and  is  used  for  making  statuary,  vases,  and  ornaments. 
Gypsum  plasters  produce  a  hard,  white  surface  of  fine  texture 
and  are  used  for  all  plastered  walls  and  ceilings  unless  intended  to 
be  covered  by  paper.  They  are  extensively  employed  in  the  follow- 
ing classes  of  construction  : 

1.  For  walls  and  ceilings,  applied  in  two  or  three  coats. 

2.  Applied  as  a  finishing  coat  over  Portland  cement  mortar. 

3.  Applied  as  a  finishing  coat  over  lime  mortar. 

4.  As  a  cement  for  ceramic  tiles,  mosaics,  etc. 
Gypsum  plasters  are  also  of  the  following  types : 

a.  Plaster  or  plaster  of  Paris. 

b.  Ready-mixed  plasters. 

c.  Keene's,  Parian,  Martin's  and  other  white  cements. 
Plaster  of  Paris  is  prepared  by  calcining  or  heating  gypsum, 

thus  driving  off  some  of  the  water  which  it  contains.  When  plaster 
is  again  mixed  with  water,  they  re-combine  to  make  gypsum  and 
the  minute  crystals  of  this  substance  in  forming,  interlace  and 
cause  the  plaster  to  set. 

Ready-mixed  plasters,  containing  plaster  of  Paris,  mixed  with  the 
proper  proportions  of  sand  for  scratch,  brown,  or  finishing  coats, 
are  put  up  by  manufacturers  in  various  parts  of  the  United  States. 
Among  the  advantages  which  are  said  to  accrue  from  their  use  may 
be  mentioned:  uniformity  in  strength  and  quality,  extra  hardness 
and  toughness,  freedom  from  pitting  and  saving  in  time. 

The  white  gypsum  cements,  such  as  Keene's,  Parian,  and  Martin's, 
are  employed  for  their  hardness  and  strength. 

The  operation  of  plastering  with  gypsum  cements  and  plasters 
is  essentially  similar  to  that  which  has  been  described  for  lime. 
From  two  to  three  coats  are  employed,  and  these  are  floated,  scoured, 
scratched,  and  trowelled,  as  in  the  case  of  lime  mortar.  Greater 
care,  however,  is  required  as  the  plaster  is  generally  either  exposed 
or  kalsomined  and  a  perfect  surface  appearance  without  seams, 
cracks,  or  flaws  is  essential. 

In  using  Parian  or  other  white  cement  on  lath-work,  exceptional 
care  must  be  observed  that  all  the  lath  nails  be  galvanized  or  painted 
over,  or  covered  with  shellac  to  prevent  rust.  For  first-coating  and 

[95] 


Handbook  for  Cement  and  Concrete  Users 

floating  ceilings  with  this  material,  the  proportions  for  best  work 
are  i  part  of  cement  to  2  of  sharp  sand,  adding  about  the  same 
quantity  of  hair  as  for  lime  plaster. 

For  the  sake  of  economy  or  for  the  purpose  of  excluding  damp- 
ness, walls  are  generally  floated  with  Portland  cement  mortar  in 
the  proportion  of  i  part  of  cement  to  3  of  sand,  and  finished  with 
neat  Parian  or  other  white  cement.  Portland  cement  is  much 
cheaper  than  Parian,  but  produces  an  efflorescence  on  the  finished 
surface,  which  is  inimical  to  successful  painting  if  attempted  before 
the  material  has  had  time  to  dry  out.  Gypsum  cements,  on  the 
other  hand,  cannot  resist  the  effects  of  moisture.  It  is,  therefore, 
imperative  that  damp  walls  should  be  floated  with  Portland  cement, 
where  a  white  cement  finish  is  desired. 

Plaster  of  Paris  is  used  as  a  finishing  coat  over  lime  mortar  to 
improve  the  appearance  of  the  surface,  and  is  also  mixed  with  the 
lime  putty  for  the  same  purpose.  When  a  harder  finish  is  desired, 
Keene's  cement  is  employed. 

Keene's  cement  is  employed  as  a  binder  for  ceramic  tiles  and 
mosaics,  although  for  exterior  work,  white  Portland  cement  is  now 
used,  on  account  of  its  superiority  when  exposed  to  the  weather. 

By  the  use  of  white  cements  a  great  saving  in  time  can  be  effected, 
as  work  can  be  begun  and  finished  in  one  operation  without  waiting 
for  the  different  coats  to  dry,  as  in  ordinary  lime  plastering.  For 
sanitary  purposes  they  are  unequalled.  This,  combined  with  their 
chemical  properties,  which  enables  them  to  be  painted,  papered,  or 
kalsomined  as  soon  as  finished,  renders  them  the  most  valuable  of 
all  plastering  materials  for  interior  work.  They  are  free-working, 
sanitary,  durable,  and  practically  fireproof,  and  when  properly 
manipulated  can  be  worked  to  a  porcelain-like  surface. 

PORTLAND  CEMENT  PLASTERS  OR  STUCCO 

Portland  cement  mortar  is  now  employed  for  external  plastering 
or  stucco  work  on  account  of  its  durability  and  resistance  to  moist- 
ure. It  is  also  used  as  a  scratch  coat  for  interior  walls  and  ceilings 
where  Parian  or  Keene's  cement  is  used  as  a  finishing  coat;  while 
white  Portland  cement  is  used  as  a  final  coat  for  both  interiors  and 
exteriors. 

[96] 


Mortars,  Plasters,  and  Stuccos 

Stucco  is  a  composite  coat,  about  i  1/2  inches  thick,  placed  on 
the  outside  of  a  building  in  one,  two,  or  three  coats.  Stucco  may 
be  applied  to  wood,  stone,  brick,  tile  or  concrete,  either  by  roughen- 
ing the  surface  or  by  means  of  wood  or  metal  lath,  supported  on 
furring  strips.  Stucco  may  be  composed  of: 

a.  Portland  cement  and  sand. 

b.  Portland  cement,  sand,  and  pebbles. 

c.  Portland  cement  and  sand  mixed  with  about  1/6  of  its  volume 
of  lime  paste. 

Moyer  also  recommends  the  addition  of  15  per  cent  of  mineral 
oil  to  the  wet  mortar,  after  the  latter  has  been  thoroughly  mixed. 

i  —  9  or>  c«nf  re 

^-Obeofbioq 


/*i~a 


-  ~K  m  b  e  r—  re  L  n  4-c  d 
r  rPJcisfcr- 


—  3  orvcenfrr- 


FIG.  27. — Application  of  Stucco  to  Frame  Building. 

Lime  mortar  is  employed,  chiefly,  when  the  stucco  is  applied  to 
stone,  the  object  being  to  prevent  hair  cracks,  retard  the  rate  of 
setting  and  render  the  mortar  easier  to  work. 

Application  of  Stucco  to  Laths. — Lime  mortar  and  gypsum 
plasters  for  interior  plastering  and  fresco  work  are  generally  applied 
to  wooden  laths  nailed  j;o  the  studding.  The  laths  are  separated 
about  3/8  of  an  inch  apart,  so  that  the  mortar  will  be  forced  into 
the  interstices  and  serve  as  a  key.  The  best  laths  are  of  split  pine. 
Oak  laths  formerly  used  are  very  liable  to  warp.  Sawn  laths  are 
cheaper  than  riven  but  are  weaker  because  of  cross-graining.  The 
defects  that  are  to  be  avoided  in  laths  are  sap,  knots,  crookedness, 
and  undue  smoothness. 

i  [97] 


Handbook  for  Cement  and  Concrete  Users 


For  exterior  work  and  for  hollow-walled  interiors,  metal  laths 
are  employed.  These  consist  of  woven  wire,  expanded  metal,  rib- 
lath,  and  other  forms  of  steel  fabric,  and  may  be  obtained  either 
painted  or  galvanized. 

Specifications  for  Lath. — Metal  lath  is  generally  specified  by 
gauge  and  it  is  always  designated  by  gauge  in  catalogues. 

All  purchasers  of  lath  should  specify  the  gauge  and  weight. 
The  weight  per  square  yard  of  the  lath  in  different  gauges  is  given 
in  the  table  below. 

TABLE  VII.— SIZES  OF  METAL  LATHS. 


Size  of  Sheet 
r  8  X  96  Inches. 

Weight  per 
Bundle. 

Yards  per 
Bundle. 

Sheets  per 
Bundle. 

Weight  per 
Yard. 

Yards  in  100 
Pounds. 

No.  27  Gauge. 

27^  Ibs. 

12 

9 

2j  Ibs. 

43 

No.  26       " 

3°      " 

12 

9 

**     " 

40 

No.  25       " 

35 

12 

9 

2.9    « 

.     34l 

No.  24       " 

40^   " 

12 

9 

3-4    " 

29§ 

TABLE  VIII. — QUANTITIES  FOR  100  SQUARE  YARDS  OF  LATH. 


Lineal  Feet 

POUNDS  I 

REQUIRED. 

Width  of  Furring. 

Material. 

per  Lb. 

12  In.  Ctrs. 

1  6  In.  Ctrs. 

^  inch  

Flat  wire. 

20 

50 

77 

Band  iron. 

20 

40 

?4 

3         « 

67 

„ 

«         « 

IO 

90 

67 

Rib-lath  is  made  by  the  Trussed  Concrete  Steel  Co.,  Detroit, 
Mich.,  and  consists  of  a  series  of  parallel  ribs  which  are  deeply 
corrugated  or  beaded.  In  application  these  ribs  act  as  small  steel 
beams  spanning  between  the  studs  and  giving  the  lath  extraordinary 
stiffness  and  rigidity.  Owing  to  this  stiffness  the  studs  may  be 
placed  a  much  greater  distance  apart  than  with  the  ordinary  forms 
of  lath,  thus  saving  in  the  cost  of  studding  and  the  labor  of  in- 
stallation. 

Rib-lath  is  so  expanded  as  to  provide  a  perfect  clinch  or  key  for 
the  plaster.  The  key  thoroughly  anchors  the  plaster  to  the  lath, 
allowing  only  a  minimum  amount  of  plaster  to  flow  through. 

[98] 


Mortars,  Plasters,  and  Stuccos 

By  the  use  of  rib  studs  and  lath,  hollow  partitions  may  be  built 
of  ample  strength  and  rigidity.  Hollow  exterior  walls  supported 
on  metal  lath  also  furnish  a  practicable  and  damp-resisting  structure, 
when  the  construction  is  properly  safeguarded. 

A  stucco  finish  possesses  many  advantages  over  the  ordinary 
wood  exterior — it  presents  a  handsome  appearance,  it  does  not 
require  painting,  and  it  is  exceedingly  durable.  Either  metal  lath 
or  wood  lath  can  be  used,  but  the  metal  is  preferable.  The  wood 
lath,  if  used,  should  be  wet  enough  to  prevent  absorption  of 
moisture  from  the  plaster,  but  not  wet  enough  to  cause  it  to  swell, 
because  it  will  shrink  again  upon  drying,  and  cause  the  plaster  to 
crack.  Green  wood  lath  is  better  than  dry. 

The  use  of  wooden  lath  should  be  restricted  to  small  and  unim- 
portant work.  In  the  case  of  small  buildings,  or  such  as  may  need 
patching,  it  offers  a  cheap  method  of  obtaining  a  pleasing  exterior, 
but  is  very  apt  to  prove  a  failure.  The  reason  is  as  follows:  If 
the  lath  is  too  dry  when  the  stucco  is  applied,  it  will  absorb  moisture 
from  the  plaster  to  the  degree  that  the  cement  will  not  set 
properly  and  in  time  the  stucco  will  fall  off.  On  the  other  hand, 
wood  made  too  wet  will  contract  when  it  becomes  dry  and  the 
same  disastrous  results  are  apt  to  follow.  For  the  reasons  given 
above  it  is  best  to  employ  a  metal  lath  where  the  importance 
of  j  the  undertaking  will  warrant  the  slight  additional  expense 
imposed  by  its  use. 

Practical  Considerations. — The  following  principles  and  rules 
should  be  taken  into  consideration  when  specifying  the  use  of 
metal  lath  for  plastering  or  stucco. 

Painting  adds  but  little  weight  to  the  lath. 

Galvanizing  adds  from  0.75  Ib.  to  0.9  Ib.  per  square  yard  accord- 
ing to  the  gauge  of  the  lath. 

Beware  of  lath  cut  from  sheets  galvanized  before  cutting  and 
expanding,  for  only  two  sides  of  the  four  in  each  strand  have  any 
galvanizing  on  them,  and  these  are  badly  cracked  and  scaled  during 
the  process  of  expanding. 

Be  sure  to  specify  the  gauge  of  the  metal  from  which  the  lath 
is  cut,  and  in  addition  thereto  the  weight  per  square  yard,  and  if 
coated  or  galvanized  add  the  weight  of  the  protection. 

Fasten  the  sheets  horizontally,  i.e.,  the  long  way  of  the  mesh 

[991 


Handbook  for  Cement  and  Concrete  Users 

being  horizontal,  so  that  the  length  of  the  sheets  is  across  the  stud- 
ding instead  of  being  placed  vertically. 

The  dip  of  the  strand  should  be  inward  and  downward,  away 
from  the  workmen,  so  that  a  perfect  key  can  be  formed. 

Grounds  should  allow  3/8  inch  over  face  of  lath.  Edges  of 
sheets  should  lap  about  the  width  of  one  mesh  and  no  more,  simply 
to  make  the  lath  stiff,  and  the  meshes  should  nest. 

When  using  metal  studding,  the  lath  will  be  fastened  in  the 
manner  provided,  which  differs  with  the  studs  made  by  different 
makers. 

When  the  lath  is  placed  on  wooden  studding,  it  is  advisable  to 
use  crimped  metal  furring  to  provide  a  key  between  the  lath  and 
the  studding,  to  maintain  a  uniform  thickness  of  plaster,  and  also 
to  prevent  the  line  of  studding  from  showing  through  the  plaster, 
owing  to  the  difference  in  the  moisture  in  the  plaster  against  the 
studding  and  that  between  adjacent  studs. 

For  walls  place  studs  12  to  16  inches  on  centres.  Twelve  inches 
is  best  for  ceiling  beams,  channels,  or  T's. 

Staples  should  be  about  5  inches  apart  and  of  sufficient  length  to 
go  through  lath  and  astride  of  furring  strip  into  the  wood  at  least 
one  inch.  When  fastened  to  metal  channels  or  T's,  galvanized  wire 
is  used. 

When  plastering  on  walls  of  brick,  concrete,  etc.,  metal  furring 
should  always  be  used. 

In  building  a  cement  stucco-finished  house  the  usual  construction 
is  completed  as  far  as  the  exterior  sheathing.  Precaution  must  be 
taken  to  make  the  framework  as  stiff  as  possible.  Often  all  the 
exterior  sheathing  is  placed  diagonally  so  that  no  swaying  will 
occur  to  crack  the  plaster,  although  metal  lath  reinforces  the  cement 
work  considerably  and  prevents  to  a  great  extent  any  surface 
cracking. 

SPECIFICATIONS   FOR   EXTERIOR    LATHING   AND   PLASTERING 
(American  Association  of  Portland  Cement  Manufacturers) 

"  Lathing. — Cover  all  exterior  walls,  etc.,  shown  for  plaster 
with  an  approved  galvanized  woven  wire  lath  secured  to  5/8-inch 
by  i -inch  furring  strips,  set  9  inches  apart,  with  i-inch  galvanized 

[100] 


Mortars,  Plasters,  and  Stuccos 

staples  every  5  inches.  All  lath  must  run  at  right  angles  to  furring, 
and  all  joints  are  to  be  made  where  they  will  be  covered  with  half 
timber,  and  joints  are  to  be  broken  every  course. 

"  Plaster. — All  walls,  etc.,  shown  on  elevation  for  plaster  to  be 
three-coat  work  on  wire  lath  as  follows:  The  first  coat  is  to  be 
composed  of  2  parts  rich  lime-mortar  and  i  part  Portland  cement, 
with  a  large  proportion  of  long  cow-hair.  The  lime-mortar  is  to 
be  mixed  four  days  before  using,  and  the  cement  is  not  to  be  added 
until  the  mortar  is  ready  to  be  used,  and  is  to  be  mixed  in  small 
quantities  as  the  work  progresses.  The  face  of  the  first  coat  must 
be  well  scratched  to  make  a  key  for  the  second  coat,  and  shall  be 
thoroughly  dry  and  surface  cracks  appear  before  the  second  coat 
is  applied.  The  second  coat  will  be  the  same  composition  as  the 
first,  except  that  the  cow-hair  is  omitted.  The  scratch  coat  will  be 
dampened  before  the  second  coat  is  applied.  The  third  coat  will 
be  the  same  as  the  second,  except  that  a  coarse  sand  will  be  used 
and  the  third  coat  will  be  floated  up  to  a  rough  finish.  All  sand 
used  in  the  exterior  work  is  to  be  approved  by  the  architect.  The 
contractor  will  be  careful  to  bring  his  plaster  work  up  perfectly  flush 
with  nailing  grounds  furnished  and  set  by  carpenter.  No  exterior 
plaster  will  be  attempted  until  the  building  is  under  roof  and  all 
interior  partitions  are  studded  up  and  braced." 

Application  of  Stucco  to  Stone. — When  stucco  is  applied  without 
the  aid  of  fabrics,  special  care  must  be  taken  to  obtain  a  sufficient 
bond.  When  applied  to  stone,  the  surface  must  be  thoroughly 
cleaned  of  all  loose  mortar  and  disintegrated  stone,  and  before  the 
plaster  is  applied  the  surface  must  be  thoroughly  wet.  The  amount 
of  wetting  necessary  depends  upon  the  character  of  the  stone  of 
which  the  house  is  built.  If  it  be  a  soft,  porous  stone,  a  great  deal 
of  water  must  be  applied,  if  it  be  a  hard,  compact  stone,  not  so  much. 
In  every  case  the  old  surface  must  be  sufficiently  saturated  so  that 
no  water  will  be  absorbed  from  the  plaster  This  is  an  important 
point,  and  one  which  is  often  overlooked,  and  many  failures  can  be 
traced  to  the  fact  that  the  surface  was  not  thoroughly  saturated  with 
water. 

There  are  several  methods  of  wetting  the  exterior  to  be  plastered. 
A  large  brush  can  be  used,  and  in  a  manner  similar  to  that  employed 
in  whitewashing  a  wall.  In  this  way  the  whole  surface  can  be  wet, 

[101] 


Handbook  for  Cement  and  Concrete  Users 

or  the  water  can  be  applied  with  a  hose.  When  a  hose  is  used,  the 
best  way  is  to  spray  the  water.  This  can  be  easily  accomplished  by 
compressing  the  end  of  the  hose.  Care  must  be  taken  to  apply  the 
plaster  at  once,  and  before  the  wall  has  had  an  opportunity  to  dry. 
If  the  plaster  is  applied  to  a  dry,  porous  surface,  the  latter  will 
take  up  so  much  water  that  the  cement  in  the  plaster  will  not  set. 
This  causes  the  plaster  to  dry  out,  crack,  and  fall  off,  and  is  usually 


FIG.  28.— Stucco  on  Hollow  Concrete  Tile  Walls. 

the  cause  of  most  of  the  unsatisfactory  results  in  the  use  of  cement 
plaster. 

Application  of  Stucco  to  Brick. — The  treatment  of  a  brick  surface 
is  very  similar  to  that  of  a  stone  exterior.  The  porous  nature  of 
the  brick,  however,  necessitates  the  utmost  care  in  wetting  before 
the  first  coat  is  applied,  or  the  results  will  not  be  satisfactory.  If 
the  brick  wall  has  been  painted  and  this  paint  is  scaling  off,  as  it 
so  often  does,  it  should  be  thoroughly  scraped  and  cleaned,  and  all 
loose  mortar  removed.  If  possible,  the  old  mortar  should  be  picked 
out  1/2  to  3/4  of  an  inch  from  the  face  of  the  brick-work,  and  when 
the  first  coat  is  applied  it  is  forced  into  these  crevices  and  forms  an 
excellent  bond.  The  comparatively  smooth  surface  of  the  brick 

[102] 


Mortars,  Plasters,  and  Stuccos 


wall  will  require  less  material  for  the  first  coat  than  a  rough  surface  of 
stone.  The  first  coat  over  the  brick-work  must  be  scratched 
thoroughly  and  allowed  to  set  until  it  is  strong  enough  to  support 
the  second  coat.  The  second  coat  is  then  applied  in  the  same  way 
as  has  been  described. 

The  original  smooth  surface  of  the  brick  wall  lends  itself  very 
readily  to  a  smooth  plaster  finish.     This  is  obtained  by  using  a 


Light  Furring 

letat  Lath 
ar\d  Plaster 


<•  Concrete! 
Piaster' 


Rods 


Stucco 

FIG.  29. — Hollow  Concrete  Tile  and  Stucco  Wall  and  Floor  Construction. 

finish  coat  containing  rather  fine  sand  and  placed  with  a  steel 
trowel.  When  it  is  desired  to  obtain  an  Old  English  style  of  ex- 
terior, the  smooth  finish  coat  is  necessary.  Very  artistic  and  de- 
sirable results  have  been  secured  by  thus  renovating  brick  exteriors. 
Stucco  on  Hollow  Tile. — Walls  of  hollow  tile  form  an  ideal 
framework  for  stucco  houses,  on  account  of  their  strength,  in- 
destructibility by  fire  and  insulation  against  heat  and  cold.  When 
properly  surfaced,  such  blocks  also  furnish  an  excellent  bond  to 
the  stucco,  so  that  plastering  can  be  applied  directly  to  the  tile 
without  furring  or  lathing.  This  bond  is  obtained  by  indenting 
or  scoring  the  surface  of  the  tiles  by  a  series  of  corrugations,  by 
leaving  the  surfaces  rough,  and  by  the  use  of  dovetailed  grooves 
to  receive  cement,  plaster,  and  stucco.  The  tile  should  in  all  cases 


Handbook  for  Cement  and  Concrete  Users 

be  well  wetted  before  applying  the  mortar,  and  if  the  weather  is 
hot,  it  will  be  necessary  to  spray  the  finished  wall  twice  a  day  for 
a  period  of  three  or  four  days  after  the  completion  of  the  work. 

Application  of  Stucco  to  Concrete. — The  treatment  of  a  concrete 
surface  that  needs  to  be  plastered  depends  upon  whether  the  wall 
is  new  or  old.  The  best  results  are  obtained  by  placing  the  plaster 
immediately  after  the  forms  have  been  removed  and  while  the 
concrete  is  still  green.  In  this  case  very  little  or  no  preparation 
of  the  concrete  is  necessary  to  receive  the  plaster,  which  is  applied 


FIG.  30. — Artistic  Garage.     Stucco  on  Pipe  Frame. 

before  the  wall  has  dried  out.  A  single  coat  is  usually  all  that  is 
required,  and  the  finish  desired  may  be  secured  in  the  same  manner 
as  with  the  final  coat  over  a  stone  or  brick  exterior.  If  the  concrete 
wall  is  old,  much  care  must  be  taken  in  preparing  it  for  the  plaster. 
The  excess  of  cement  likely  to  have  flushed  to  the  surface  must  be 
removed  and  the  surface  thoroughly  cleaned  and  well  wet  before 
applying  the  plaster,  or  it  will  crack  and  fall  off.  By  the  use  of 
facing  forms,  new.  wall's  may  be  constructed  in  which  the  plaster 
finish  and  concrete  wall  are  carried  up  simultaneously,  resulting  in 
a  perfect  bond  between  the  two. 

[  104] 


Mortars,  Plasters,  and  Stuccos 

Renovating  Frame  Buildings. — Old  frame  buildings  can  be 
readily  renovated  by  the  use  of  cement  stucco.  The  exterior  is 
covered  with  lath  furred  out  as  already  described  and  either  two 
or  three  coats  are  applied.  In  such  a  case  it  is  necessary  to  bring 
out  the  door  and  window  trim  unless  the  plaster  is  to  finish  flush 
with  the  old  trim,  or  if  it  is  desired  to  keep  the  old  frames  and  have 
them  project,  it  will  be  necessary  to  remove  the  old  siding  and  staple 
the  furring  directly  to  the  old  studding.  Frequently  the  trim  is 
removed  and  the  lath  brought  around  the  casing,  thus  getting  a 
recessed  window  with  no  wood  showing. 

Quantities  of  Materials  for  Stucco. — The  quantities  of  cement  and 
sand  required  for  stucco  work  vary  with  the  thickness  of  the  coat 
and  the  proportions  of  the  ingredients.  The  following  table  shows  the 
covering  power  of  a  barrel  of  cement  when  made  into  mortar  for 
thicknesses  varying  from  1/2  to  i  inch,  and  for  proportions  varying 
from  i  :  i  to  i  :  3  mixtures  of  cement  and  sand. 


TABLE  IX. — AREA  COVERED  BY  MORTAR. 

Produced  from  One  Barrel  of  Portland  Cement  Mortar  (3.8  cu.  ft. 
Cement  Paste).     No  Lime. 


Composition  of  Mortar. 

Thickness  of  Coat. 

Square  Feet  of  Area 
Covered. 

i  Cement,  i  Sand.   .    .          J 

i  inch 

3        " 

6? 
oo 

I 
i  Cement,  2  Sand  •< 

i  inch 
f     " 

134 

104 

i  Cement,  3  Sand.         .          .                  .  .  ^ 

1           (C 

i  inch 
1     " 

208 

140 

187 

i     « 

280 

105 


CHAPTER  XII 

THE    ARTISTIC    TREATMENT    OF    CONCRETE 
SURFACES 

Imperfections  in  Concrete  Surfaces. — Methods  of  Finishing  Surfaces. — Spading. — 
Stucco. — Mortar  Facing. — Grouting. — Scrubbing  and  Washing. — Etching. — 
Tooling. — Selected  Aggregates. — Tinting  and  Coloring. — Panelling,  Mosaics, 
Carving,  etc. — Prevention  of  Cracking  and  Crazing. 

CONCRETE  is  a  plastic  material  which  can  be  moulded  and  mod- 
elled at  will,  and  as  such  the  temptation  is  strong  to  cast  it  into  forms 
strongly  suggestive  of  some  other  material.  "  Beauty,  however, 
in  structural  design  is  worthy  the  name  only  when,  like  beauty  in 
Nature,  it  has  character.  It  must  not  be  a  servile  copy  of  the  style 
peculiar  to  some  other  material,  but  in  fact  must  express  its  own 
individuality  without  dissimulation."  * 

Imperfections  in  Concrete  Surfaces. — Good  design  requires  that 
the  surface  must  be  finished  so  as  to  produce  a  pleasing  effect.  In 
many  concrete  structures  the  surface  is  irregular,  uneven  in  texture, 
and  stained  or  discolored  or  of  lifeless  hue.  Imperfections  in  the 
surface  of  concrete  are  due  to  -one  or  more  of  the  following  causes : 

1.  Imperfectly  made  forms. 

2.  Carelessly  mixed  or  placed  concrete. 

3.  Use  of  forms  with  dirt  or  cement  adhering  to  the  boards. 

4.  Efflorescence  and  discoloration  of  the  surface. 

5.  Shrinkage  cracks,  and  crazing  of  surface. 

In  well  mixed  and  placed  concrete,  the  film  of  cement  paste 
which  flushes  to  the  surface  will  take  the  impress  of  every  flaw  in 
the  surface  of  the  forms.  It  will  even  show  the  grain  marks  in  well- 
dressed  lumber. 

Joint  marks  may  be  eliminated  wholly  or  in  part  by  pointing 
the  joints  with  clay  or  mortar  or  by  pasting  strips  of  paper  or  cloth 
over  them.  Grain  marks  and  surface  imperfections  can  be  reduced 
by  oiling  the  lumber  so  as  to  fill  the  pores  or  by  first  oiling  and  then 
filling  the  coat  of  oil  with  fine  sand  blown  against  the  boards. 

*  A.  O.  Elzner  on  "  The  Artistic  Treatment  of  Concrete." 
[106] 


Artistic  Treatment  of  Concrete  Surfaces 

Imperfectly  mixed  and  placed  concrete  gives  irregularly  colored, 
pitted,  and  honeycombed  surfaces  with  here  a  patch  of  smooth 
mortar  and  there  a  patch  of  exposed  stone.  Careful  mixing  and 
placing  will  avoid  this  defect.  Spading  forks  should  be  used  to 
£ull  the  coarse  stones  back  and  cause  the  mortar  to  flush  to  the 
surface.  Surface  coatings  can  also  be  used  to  cover  up  any  defects. 

Efflorescence  is  the  term  applied  to  the  whitish  or  yellowish 
accumulations  which  often  appear  on  concrete  surfaces.  Efflores- 
cence is  due  to  certain  salts  leaching  out  of  the  concrete  and 
accumulating  into  .thin  layers  after  the  water  has  evaporated.  It 
is  most  troublesome  at  horizontal  joints  where  new  work  is  placed 
on  concrete  that  has  already  set.  Scrubbing  the  top  surface  with 
wire  brushes  and  flushing  it  with  a  hose  before  the  new  work  is 
started  is  the  best  preventative. 

Where  the  efflorescence  extends  over  the  surface  of  the  wall,  it 
may  (i)  be  covered  up  by  the  use  of  cement  coatings  or  water- 
proofing compounds,  (2)  or  removed  by  scraping  and  chipping  or 
(3)  washed  away  with  acids.  Muriatic  acid  is  generally  used  for 
this  purpose.  It  is  diluted  with  4  or  5  times  its  bulk  of  water  and 
applied  with  scrubbing  brushes.  Water  should  also  be  played  with 
a  hose  on  the  concrete  while  being  cleaned  to  prevent  penetration 
of  the  acid.  The  cost  of  scrubbing  with  acid  is  from  30  cents  to 
50  cents  per  square  yard.  The  question  of  efflorescence  is  further 
discussed  in  Chapter  XXX. 

METHODS  OF  FINISHING  SURFACES 

The  usual  methods  of  finishing  concrete  surfaces  are  as  follows: 

1.  Spading  and  trowelling  the  surface. 

2.  Facing  with  stucco. 

3.  Facing  with  mortar. 

4.  Grouting. 

5.  Scrubbing  and  washing. 

6.  Etching  with  acid. 

7.  Tooling  the  surface  with  bush-hammers  or  other  tools. 

8.  Surfacing  with  gravel  or  pebbles. 

9.  Tinting  the  surface. 

10.  Panelling,  mosaics,  carving,  etc. 


Handbook  for  Cement  and  Concrete  Users 

Spading  and  Trowelling. — With  wet  concrete  and  ordinarily 
good  form  construction  a  reasonably  good  surface  appearance  may 
be  obtained  by  pushing  a  spade  down  between  the  lagging  and  the 
fresh  concrete  and  pulling  back  the  stones,  so  that  the  grout  can 
flush  to  the  surface.  Trowelling  should  be  done  while  the  concrete 
is  still  green.  In  this  condition  the  edges  of  copings,  etc.,  can  be 
rounded  by  edging  tools  such  as  are  used  for  finishing  cement 
sidewalks. 

Facing  with  Stucco. — When  properly  applied,  stucco  finishes 
are  most  pleasing  and  artistic,  especially  for  residences.  By  the 
use  of  white  Portland  cement,  white  sand  or  crushed  marble,  a  most 
beautiful  effect  can  be  produced.  Cream-colored  or  other  delicate 
tints  can  also  be  obtained  by  mixing  pigments  with  the  cement  or 
by  the  use  of  colored  sand  and  gravel.  The  most  successful  stucco 
finishes  are  as  follows : 

a.  Smooth  float. 

b.  Rough  cast. 

c.  Slap-dash  finish. 

d.  Pebble-dash  finish. 

A  smooth  float  finish  on  a  building  is  always  pleasing,  especially 
when  white  or  delicately  tinted  materials  are  used.  Such  finishes 
are  ordinarily  produced  with  a  wooden  float.  Floats  should  be 
made  of  hard,  close-grained  timber  such  as  beech  or  birch,  and 
should  be  drawn  straight  along  the  wall,  without  twisting  or  turning. 
Smoother  finishes  can  be  obtained  by  the  use  of  steel  trowels  or  with 
wooden  floats  covered  with  felt.  Trowelling  brings  the  neat  cement 
to  the  surface  while  the  float  tends  to  bring  out  the  grains  of  sand. 
In  Germany  by  the  use  of  felt-covered  floats  beautiful  effects  have 
been  obtained,  and  this  method  is  used  to  some  extent  in  the  United 
States,  although  the  tendency  in  this  country  is  in  the  direction  of 
rougher  finishes. 

A  rough  cast  surface  is  one  of  the  most  pleasing  finishes  and  is 
especially  appropriate  for  residences,  rustic  bridges,  and  suburban 
villas.  A  rough  cast  surface  can  best  be  put  on  with  a  broom  dipped 
into  a  solution  of  mortar,  half  and  half,  or  two  of  sand  to  one  of 
cement,  and  applied  by  stepping  back  a  distance  of  two  or  three 
feet  from  the  wall  and  striking  the  broom  with  the  hand  in  such  a 
way  as  to  drive  the  mortar  against  the  wall,  on  which  it  collects  like 

[108] 


Artistic  Treatment  of  Concrete  Surfaces 

raindrops.  The  cement  crystallizes  and  adheres  firmly  to  the 
wall.  By  the  use  of  white  mortar,  a  sparkling,  glistening  effect 
is  obtained. 

The  slap-dash  finish  is  pleasing  on  account  of  the  variety 
and  the  light-and-shade  effects  which  are  obtained.  It  is  especially 
adapted  to  foundation  courses  and  to  suburban  houses.  It  is  applied 
by  stepping  back  a  distance  of  two  or  three  feet  from  the  wall  and 
throwing  the  mortar  against  the  surface  with  a  trowel.  For  its 
successful  applications,  the  workman  must  possess  considerable 
skill  and  the  scratch-coat  to  which  it  is  attached  should  not  have 
attained  too  great  a  set  to  prevent  bond. 

The  pebble-dash  finish  is  well  adapted  to  foundation  courses, 
rustic  bridges,  etc.  It  is  obtained  by  embedding  round  half-inch 
pebbles  in  the  finishing  coat.  Excellent  effects  are  obtained  with 
white  quartz  pebbles,  and  warm  effects  with  colored  stones  or 
gravel.  The  pebbles  should  be  of  uniform  size  and  tossed  into  the 
cement  mortar  so  as  to  be  half  exposed. 

Stucco  finishes  may  by  proper  bonding  be  applied  to  any  surface, 
whether  of  wood,  stone,  or  concrete.  They  are  also  well  adapted 
to  the  renovation  of  old  buildings,  as  well  as  to  the  embellishment 
of  new  structures.  Unless,  however,  the  stucco  is  keyed  to  the 
underlying  material  by  means  of  metal  laths  or  fabrics,  such  finishes 
when  applied  to  concrete  are  lacking  in  adhesive  properties  and  one 
of  the  following  methods  which  are  especially  adapted  to  concrete, 
should  preferably  be  employed. 

Facing  with  Mortar. — A  facing  mortar  of  cement  and  sand  is 
used  in  thicknesses  of  from  i  to  2  inches  when  a  surface  finish  of 
fine  texture  or  of  some  special  color  or  composition  is  desired. 
When  this  is  used  the  mortar  facing  and  the  concrete  backing  should 
be  constructed  simultaneously  in  order  to  obtain  a  perfect  bond. 
This  is  usually  accomplished  by  the  use  of  facing  forms,  which  are 
placed  temporarily  the  proper  distance  back  of  the  lagging;  after 
which  the  facing  mortar  is  tamped  into  the  narrow  space  between 
the  two  forms,  the  body  of  the  wall  is  poured,  the  facing  form  raised, 
and  both  backing  and  facing  thoroughly  bonded  by  tamping  them 
together. 

Grout  finishes  serve  only  to  fill  the  small  pits  and  pores  in  the 
surface  coating.  Cavities  or  joint  lines  must  first  be  removed  by 

[109] 


Handbook  for  Cement  and  Concrete  Users 

plastering  or  rubbing.  The  grout  is  then  applied  with  a  brush,  and 
should  have  the  consistency  of  whitewash.  A  i :  2  mixture  of  cement 
and  sand  is  often  used.  Where  a  dark  finish  is  desired,  a  grout  is 
made  by  mixing  neat  cement  and  lampblack  in  equal  parts. 

Scrubbing  and  Washing. — The  use  of  granite  chips,  colored 
stones,  white  pebbles,  and  other  special  aggregates,  affords  a  success- 
ful finish  for  concrete  structures.  This  consists  in  removing  the  forms 
while  the  concrete  is  still  green,  and  then  scrubbing  the  surface  with 
wire  brushes  and  water  until  the  film  of  cement  has  been  removed, 
and  the  clean  sand  and  stone  exposed.  Warm  tones  can  be  secured 
by  the  use  of  crushed  brick  or  red  gravel ;  a  dark  colored  stone  with 
light  sand  gives  a  color  much  resembling  granite;  fine  gravel  or 
coarse  sand  gives  a  texture  like  sandstone. 

There  is  no  artistic  reason  for  allowing  only  the  bonding  material 
to  be  displayed  to  the  eye.  On  very  large  jobs  the  surface  can  be 
cleaned  off  by  means  of  a  sand  blast,  and  on  smaller  jobs  the  surface 
may  be  cleaned  exposing  each  grain  of  sand  by  means  of  muriatic 
acid  in  dilute  solution,  i  part  commercial  muriatic  acid,  to  4  to  5 
parts  clear  water. 

Where  white  aggregates  are  used  the  surface  may  be  cleaned 
off  with  a  solution  of  sulphuric  acid,  i  part  acid,  4  to  5  parts  clear 
water.  The  sulphuric  acid  leaves  a  white  deposit  and  therefore 
should  not  be  used  excepting  where  the  aggregates  are  white. 

Another  method  is  to  scrub  the  surface  while  yet  green,  say 
within  24  hours,  with  a  house  scrubbing  brush  and  clear  water. 
This  is  more  difficult  than  the  others  for  the  reason  that  if  the  stucco 
is  allowed  to  remain  too  long  before  scrubbing,  it  will  be  too  hard 
to  remove  the  coat  of  neat  cement  from  the  outside  of  each  particle 
of  sand  or  other  aggregates;  and  if  scrubbed  when  it  is  too  soft, 
the  surface  may  be  damaged  and  difficult  to  repair. 

If  the  character  of  the  available  aggregates  will  not  present  a 
pleasing  surface  when  exposed,  the  following  surface  treatment 
may  be  used  as  recommended  by  Moyer. 

While  the  last  coat  is  still  thoroughly  damp,  apply  a  Portland 
cement  paint  composed  of  i  part  Portland  cement,  12  per  cent  of 
the  volume  of  the  cement  of  well  hydrated  lime  in  pulverized  form, 
r  part  of  the  volume  of  the  cement  of  fine  white  sand.  Mix  with 
water  to  the  consistency  of  cream  or  the  ordinary  cold  water  paint. 

[no] 


Artistic  Treatment  of  Concrete  Surfaces 

Stir  constantly  and  apply  by  using  a  whisk  broom,  throwing  this 
paint  on  with  some  force. 

Keep  this  finish  surface  damp  for  at  least  six  days  or  longer  if 
economy  will  permit.  Do  not  allow  it  to  dry  out  in  any  one  place 
during  the  week.  If  necessary  protect  by  hanging  tarpaulins  and 
using  a  fine  spray  of  water  playing  on  several  times  during  the  day 
by  means  of  a  hose.  This  will  give  a  pleasing  light  gray  color  of 
excellent  texture. 

In  the  construction  of  monolithic  concrete  masonry  for  bridges 
for  the  city  of  Philadelphia,  it  is  the  practice  to  use  a  fine  concrete 
or  granolithic  face  composed  of  i  cement;  2  bank  sand,  and 
3  crushed  and  cleaned  black  slaty  shale,. of  the  size  commonly 
used  for  roofing, — say  one-fourth  to  three-eighths  inch.  The 
mixture  is  placed  against  the  face  forms  and  the  body  concrete  is 
poured  behind  and  both  removed  together  immediately.  In  general 
the  washing  is  done  on  the  day  following  that  on  which  the  concrete 
was  deposited,  and  an  ordinary  house  scrubbing  brush  with  a  free 
flow  of  water  is  used.  When  the  surface  is  too  hard  for  the  scrubbing 
brush,  a  wire  brush  is  first  employed,  then  a  small  block  of  wood  or  a 
brickbat  with  water  and  sand  in  order  to  cut  the  film.  If  the  surface 
has  hardened  so  as  to  require  the  grinding  action  of  the  sand  and 
block,  the  aggregate  will  not  be  brought  into  very  decided  relief  and 
the  face  will  therefore  be  comparatively  smooth.  In  cold  weather 
when  crystallization  proceeds  slowly  the  forms  may  require  to 
remain  two  days  before  the  washing  can  be  done  with  safety,  and  in 
very  cold  weather  they  have  been  left  a  whole  week,  and  the  scrub- 
bing was  successful.  In  general,  however,  the  aggregate  is  best 
brought  out  by  scrubbing  as  soon  after  the  concrete  has  been  placed 
as  possible. 

Etching  with  Acid. — Etching  with  acid  is  a  further  development 
of  the  scrubbing  process,  and  is  also  employed  for  the  purpose  ol 
removing  the  outer  skin  of  cement  and  exposing  the  aggregate.  It 
consists  in  first  washing  the  surface  with  dilute  muriatic  acid,  and 
then  with  an  alkaline  solution  to  remove  all  free  acid;  and  finally 
with  clean  water  in  sufficient  volume  to  cleanse  and  flush  the  surface 
thoroughly.  The  operation  is  simple  and  always  effective.  It 
can  be  done  at  any  time  after  the  forms  have  been  removed,  im- 
mediately or  within  a  month  or  more.  It  requires  no  skilled  labor— 

[in] 


Handbook  for  Cement  and  Concrete  Users 

only  judgment  as  to  how  far  the  acid  or  etching  process  should  be 
carried.  It  has  been  applied  with  equal  success  to  trowelled  sur- 
faces, like  pavements,  to  moulded  forms,  such  as  steps,  balusters, 
coping,  flower  vases,  etc.,  and  to  concrete  placed  in  forms  in  the 
usual  way.  It,  of  course,  means  that  in  the  concrete  facing  only 
such  material  shall  be  used  as  will  not  be  affected  by  acid,  such  as 
sand  or  crushed  granite.  Limestone  cannot  be  used,  as  it  is 
disintegrated  by  the  acid.  The  treated  surface  can  be  made  of 
any  desired  color  by  selection  of  colored  aggregates  or  by  the 
addition  of  mineral  pigments.  The  colors  obtained  by  the  selection 
of  colored  stone  are  perhaps  the  most  agreeable  and  are  doubtless 
the  more  durable. 

Tooling. — Concrete  surfaces  may  be  bush-hammered  or  other- 
wise tool-finished  like  natural  stone.  To  secure  good  results, 
however,  the  concrete  should  be  at  least  30  days  old  before  it  is 
worked.  The  cost  runs  from  3  to  12  cents  per  square  foot,  accord- 
ing to  the  character  of  the  work. 

Tooling  is  also  done  with  an  axe,  pick,  chisel,  or  pneumatic 
hammer.  The  tool  should  be  light,  and  the  blows  only  heavy 
enough  to  " scalp"  the  work,  heavy  tools  and  blows  being  liable  to 
"stun"  the  concrete,  particularly  at  or  near  the  edges.  This 
scalping  partially  exposes  the  material  of  the  aggregate,  but  does 
not  clean  it.  The  complete  exposure  and  cleansing  will  come  with 
time  and  exposure  to  the  weather  if  the  work  be  outdoors;  or  the 
action  of  the  elements  can  be  anticipated  by  washing  the  tooled 
surface  with  a  half-and-half  dilution  of  muriatic  acid,  which  of 
course  must  be  thoroughly  rinsed  off. 

Another  method  of  tooling  consists  in  removing  the  skin  with  a 
coarse-grained  emery  or  carborundum  wheel.  The  skin  is  cut 
about  as  quickly  as  the  block  can  well  be  passed  over  the  wheel. 
This  method  is  well  adapted  to  the  surfacing  of  moulded  blocks, 
slabs,  and  artificial  stone. 

Selected  Aggregates. — An  effective  variation  of  the  ordinary 
stone  concrete  surface  is  secured  by  using  an  aggregate  of  rounded 
pebbles  of  nearly  uniform  size,  and  by  scrubbing  or  etching  to  remove 
the  cement  enough  to  leave  the  pebbles  about  half  exposed  to  view. 
This  gives  a  finish  similar  to  that  obtained  in  pebble-dash  stucco 
work  and  is  very  pleasing,  especially  for  rustic  bridges  and  cottages. 

[112] 


Artistic  Treatment  of  Concrete  Surfaces 

The  scrubbing  is  best  done  when  the  concrete  is  24  hours  old,  at 
which  time  the  outer  skin  is  readily  removed.  Where  the  forms  are 
required  to  remain  in  position  for  a  longer  period,  as  in  the  case  of 
arch  or  girder  forms,  the  acid  treatment  is  required. 

Tinting  and  Coloring. — The  use  of  colored  or  tinted  surfaces 
includes : 

a.  Pure  white  or  cream-colored  tints. 

b.  Colors  produced  by  the  use  of  pigments. 

c.  Colors  obtained  from  the  use  of  colored  aggregates. 

d.  Colors  produced  by  painting  the  surface. 

White  surfaces  are  readily  obtained  by  the  use  of  white  Portland 
cement,  mixed  with  either  white  sand,  crushed  white  quartz,  ground 
marble,  or  ground  white  limestone.  White  surfaces  when  scrubbed 
or  acid-etched  present  a  pure  sparkling  appearance  of  rare  beauty 
when  touched  by  sunlight,  and  are  used  extensively  by  architects 
for  suburban  residences.  The  use  of  white  cements  and  aggregates 
also  permits  the  use  of  delicate  tints,  which  are  obtained  either  by 
the  use  of  pigments  or  colored  aggregates. 

Pigments  which  are  unaffected  by  the  action  of  lime  or  cement 
are  now  obtainable  for  the  purpose  of  tinting  concrete,  facing  mortar 
and  stucco.  Blue,  red,  green,  and  yellow  pigments  cost  from  8 
to  30  cents  per  pound,  and  by  proper  mixture  the  intermediate 
shades  may  be  obtained.  The  quantity  of  pigment  required  is 
from  2  to  3  per  cent  of  the  mixture  by  weight  in  order  to  produce  a 
well  colored  mortar.  The  following  table  (Table  X)  is  recom- 
mended in  the  bulletins  of  the  American  Association  of  Portland 
Cement  Manufacturers. 

In  painting  concrete  surfaces,  the  material  employed  should 
either  be  neutral,  free  from  saponifying  oil,  or  the  surface  to  be 
painted  should  be  previously  neutralized  with  dilute  sulphuric  acid 
in  order  to  convert  the  free  lime  into  gypsum.  If  such  precau- 
tion be  neglected,  the  oil  and  free  lime  will  react  chemically  and 
form  soap  which  will  destroy  the  paint. 

Coloring  by  the  use  of  Selected  Aggregates. — Many  engineers  and 
architects  prefer  to  color  their  concrete  by  the  use  of  colored  sand 
and  gravels  in  the"  mortar  which  are  exposed  by  scrubbing  and 
etching.  While  this  treatment  is  more  expensive  than  the  use  of 
colored  facing  mortars,  the  colors  are  more  permanent,  and  the  acid 

8  [113] 


Handbook  for  Cement  and  Concrete  Users 


etched  surface  exhibits  more  life  and  variety.  Excellent  effects  are 
produced  by  mixing  the  cement  with  screenings  produced  by 
crushing  a  natural  stone  of  the  desired  color. 

Panelling. — In  the  construction  of  buildings,  a  simple  and 
dignified  variation  in  the  surface  treatment  is  obtained  by  the  use 
of  panels  or  freehand  modelling.  "In  the  case  of  panels  it  is  best 

TABLE  X. — MATERIALS  USED  IN  COLORING  MORTARS.* 


Pounds  of  Color  to  100 
Pounds  of  Cement. 

Pounds  Color 
to  Barrels  of 
Cement. 

Color. 

Mineral. 

I 

2 

3 

Gray 

Germantown  Lamp  Black 

1-4 

1-2 

2 

Black  

Manganese  Dioxide. 

12 

48 

Black 

Excelsior  Carbon  Black 

2 

Blue     

Ultramarine 

tr 

s  to  6 

2O 

Green  

Ultramarine  Green 

6 

6 

24 

Red    

Iron  Oxide 

6 

6  to  10 

24 

Bright  Red  

Pompeian  or  English  Red 

6 

6 

24 

Sandstone  

Red-Purple  Oxide  of  Iron 

6 

24 

Violet  

Violet  Oxide  of  Iron 

6 

24 

Brown  

Roasted    Iron     Oxide    or 

Brown  Ochre 

6 

6 

24 

Yellow  or  Buff. 

Yellow  Ochre 

6 

6  to  10 

24 

and  simplest  to  adopt  sunken  work,  as  this  can  readily  be  produced 
by  merely  planting  a  board  or  block  of  desired  shape  against  the 
inside  face  of  form  work  which  leaves  its  impress  upon  being  re- 
moved from  the  concrete.  Or  else  a  reverse  mould  made  of  some 
artistic  bit  of  carving  for  a  panel  or  over  a  door  or  window,  or  a 
frieze,  etc.,  may  be  nailed  against  the  forms,  and  the  resulting 
impress  will  be  thoroughly  effective,  although  a  much  higher  artistic 
value  would  be  due  such  work  if  it  were  modelled  by  hand  directly 
in  the  cement  mortar  as  it  is  applied  and  before  it  has  had  a  chance 
to  harden. 

"This  sort  of  work  is  being  done  extensively  and  successfully 
in  Germany,  where  the  modern  style 'of  'Nouyeau  Art'  presents 
abundant  opportunities  for  endless  designs.  It  is  already  finding 

*  Differences  are  due  to  different  authorities  quoted. 


Artistic  Treatment  of  Concrete  Surfaces 

much  favor  in  our  own  country,  and  ought  to  reach  a  high  degree  of 
development." 

Ornamenting  Surfaces  with  Mosaics,  Carving,  etc. — Mosaics, 
similar  to  those  made  with  colored  glass  and  lead  outlines,  can  be 
made  with  burned  clays  and  cement  outlines.  Patterns  from  one 
foot  to  twenty  feet  in  diameter  have  been  made,  simply  by  burning 
slabs  of  clay  in  many  colors,  either  glazed  or  unglazed,  and  cutting 
the  slabs  into  such  shapes  as  to  show  the  outline  of  an  artistic  design. 
These  parts  are  assembled  in  a  bed  of  cement,  a  bead  being  left 
between  the  pieces  of  clay  similar  to  the  lead  bead  of  glass  windows. 
This  bead  shows  the  outline  of  the  design,  its  width  being  propor- 
tional to  the  size  of  the  figure.  As  it  becomes  increasingly  wide, 
the  figure  becomes  more  and  more  conventional.  These  cement 
outlines  can  be  colored  black  or  red,  but  as  a  rule  the  best  results 
are  obtained  with  the  natural  dead  gray,  as  it  harmonizes  with  all 
the  colors  of  the  clay. 

These  decorative  inlays  or  mosaics  are  very  beautiful  over 
mantels  and  fireplaces  as  an  inside  decoration,  and  are  also  used 
to  break  up  wall  surfaces  in  exterior  work. 

Many  other  substances  besides  clay  have  been  used  in  this  way, 
such  as  tiles,  papier  mache,  etc.,  with  more  or  less  success. 

Another  method  sometimes  used  to  ornament  the  surface  of 
mouldings,  cornices,  etc.,  while  concrete  is  green,  is  to  press  blocks 
of  wood,  cut  to  desired  shapes,  such  as  the  classical  "leaf  and  dart," 
"  beads  and  reels,"  or  any  simple  figure,  into  the  green  concrete, 
thus  leaving  a  shallow  imprint  in  the  surface.  These  imprints  can 
be  spread  at  appropriate  intervals  along  a  frieze  or  moulding,  and 
produce  very  beautiful  appearances. 

Templets  moulded  in  clay  or  cut  out  of  sheet  iron  can  be  used 
in  place  of  the  carved  wood,  if  desired. 

Concrete  surfaces  can  also  be  economically  decorated  by  carving 
before  the  concrete  has  set.  As  soon  as  the  concrete  is  sufficiently 
hard  to  resist  the  imprint  of  the  thumb  nail,  the  forms  are  removed, 
and  the  design  is  carved  out  with  sharp  steel  tools  of  proper  shape 
very  much  as  wood  is  carved.  In  this  way,  scrolls  and  floral 
designs  can  be  accomplished  with  less  skill  and  very  much  less  time 
than  in  cut-stone  work. 

Prevention  of  Cracking  and  Crazing  of  Surfaces. — The  following 

["5] 


Handbook  for  Cement  and  Concrete  Users 

is  quoted  from  Mr.  Albert  Meyer's  article  on  this  subject,  to  which 
he  has  given  a  great  deal  of  study : 

"It  has  been  known  for  some  time  that  a  very  wet  mixture  of 
concrete  is  more  apt  to  craze  and  show  these  undesirable  hair  cracks 
than  a  medium  dry  mixture  of  concrete. 

"Neat  cement,  or  the  richer  mortars,  are  found  to  be  much  more 
liable  to  hair  cracks  and  crazing  than  mortars  containing  a  larger 
proportion  of  sand  or  finely  crushed  stone.  This  is  particularly 
true  in  the  manufacture  of  cement  stone  by  the  use  of  sand  moulds 
in  which  the  mixture  is  poured  very  wet.  It  has  also  been  noted 
that,  when  the  stone  is  properly  seasoned  by  keeping  the  surface 
covered  with  a  thick  layer  of  very  wet  sand,  or  when  the  stone  is 
immersed  entirely  and  for  some  time  in  water,  the  trouble  has  been 
overcome  almost  entirely. 

"In  the  past  this  trouble  has  been  partially  overcome  by  brush- 
ing off  the  surface  of  the  concrete  or  cement  stone  with  a  stiff  steel 
brush;  or  by  scrubbing  the  surface  with  a  cement  brick  and  wet 
sand  or  carborundum  stone,  thus  partially  removing  what  might 
be  termed  a  neat  cement  face.  It  has  been  found,  however,  that 
this  does  not  entirely  overcome  the  trouble,  the  remedy  proving 
but  temporary,  the  cracks  appearing  several  months  afterward. 
The  brushing  or  scrubbing  is  merely  an  assistance;  the  real  remedy 
lies  in  keeping  the  surface  thoroughly  and  continuously  wet  as  long 
as  possible. 

"It  is  desirable  to  have  the  surface  of  the  concrete  or  cement 
stone  as  near  the  same  texture  as  the  body  of  the  concrete.  The 
exterior  should  then  be  kept  wet  by  the  application  of  wet  sand, 
clean  sawdust,  hay,  etc.,  sprinkled  from  time  to  time  with  water  or 
hanging  wet  cloths  over  the  perpendicular  surfaces,  keeping  the 
exterior  wet  and  the  cloths  wet  by  sprinkling,  or  by  any  other  method 
which  will  accomplish  this  result  and  supply  similar  or  same  con- 
ditions as  when  hardened  under  water.  By  so  doing  not  only  is 
crazing  avoided,  but  a  stronger,  tougher,  and  harder  concrete  is 
obtained.  It  is  reasonable  to  conclude  that  if  so  treated  the  surface 
will  slightly  expand,  but  not  to  a  greater  extent  than  the  body  of 
the  concrete  which  is  already  wet. 

"Hair  cracks  may  be  avoided  by  the  addition  of  mineral  oil  to 
the  wet  mixed  concrete. 


Artistic  Treatment  of  Concrete  Surfaces 


"Mineral  oils  added  to  wet  mixed  concrete  and  the  concrete 
immediately  remixed  has  the  effect  of  emulsifying  the  oils.  The 
proportion  of  oil  used  should  be  10  to  15  per  cent  of  oil  to  the  weight 
of  the  cement.  Oil  weighs  from  7  1/2  to  8  pounds  per  gallon. 

"This  oil-mixed  concrete,  when  hard,  appears  to  be  non-evap- 
orative, indicating  that  the  emulsifying  oils  held  all  the  excess  water 
in  the  mortar  or  concrete,  keeping  the  cement  particles  moist  until 
the  water  had  been  taken  up  in  crystallization  and  ultimate  strength 
reached.  Thus  similar  conditions  are  supplied  as  apply  to  concrete 
set  under  water." 

In  this  chapter  the  readier  methods  that  can  be  employed  in 
producing  artistic  effects  have  been  considered.  "This  humble 
material,  so  replete  with  possibilities,  but  as  yet  so  little  understood, 
is  manifestly  destined  to  take  an  important  place  in  the  construction 
of  our  buildings  and  must  therefore  strongly  influence  their  design." 
Our  leading  architects  are  beginning  to  find  in  concrete  a  new  and 
useful  friend,  and  with  its  help  will  evolve  a  new  architecture  that 
will  be  full  of  life  and  character,  strength  and  dignity  and  all  else 
that  goes  to  make  up  a  living  style." 

*  "  The  Artistic   Treatment  of  Concrete,"  by  A.  O.  Elzner,  in   Proceedings  of 
the  National  Association  of  Cement  Users,  1907. 


SECTION  III 

THE  MAKING  OF  CONCRETE 
PRODUCTS  IN  THE  SHOP 


CHAPTER  XIII 

CONCRETE  BUILDING  BLOCKS 

Advantages  and  Disadvantages  of  Concrete  Blocks. — Materials  for  Concrete  Blocks. — 

Types  of  Blocks. — Block  Machines. — Making  the  Blocks. — Coloring  the  Blocks. — 

Waterproofing  the  Blocks. — Building  Details. — Cost  of  Blocks. — Objections  to 

Concrete  Blocks  and  Remedies  for  Same. — Table  of  Concrete  Block  Data. — 

•   Concrete  Tiles,  etc. — Specifications  for  Concrete  Blocks. 

THE  concrete  products  manufacturing  industry  has  had  a  very 
phenomenal  growth,  and  in  fact,  the  growth  has  been  too  rapid  for 
the  good  of  the  business,  as  it  has  caused  a  large  volume  of  poor 
products  to  be  placed  upon  the  market  and  the  disrepute  into  which 
much  of  the  industry  had  fallen  on  account  of  this,  has  not  yet  been 
fully  removed;  the  tendency  now,  however,  is  toward  better  products 
and  with  renewed  confidence  due  to  wider  experience  and  the  law 
of  the  survival  of  the  fittest,  we  expect  to  see  an  accelerated  increase 
in  all  lines  of  manufactured  concrete. 

The  use  of  concrete  blocks  as  a  substitute  for  wood,  brick,  and 
stone  has  become  very  extensive.  Concrete  blocks,  when  properly 
made  and  used,  form  an  excellent  material  for  building  construction. 
They  commend  themselves  for  their  cheapness  when  compared 
with  brick  and  stone,  and  their  greater  durability  when  compared 
with  wood;  they  also  possess  the  advantage  over  the  latter  of  being 
fireproof. 

When  concrete  was  first  applied  to  building  construction,  it 
was  used  to  build  monolithic  walls.  The  idea  of  making  a  wall 
hollow  for  the  sake  of  economy,  or  for  prevention  of  moisture  or 
frost  working  through  the  wall  was  a  later  development.  At  the 
present  time  practically  the  whole  concrete-block  industry  aims  to 

[118] 


Concrete  Building  Blocks 

produce  a  wall  made  of  hollow  blocks,  with  continuous  air  chambers, 
or  of  blocks  which,  though  not  themselves  hollow,  can  be  laid  so  as 
to  produce  a  hollow  wall. 

Advantages  of  Concrete  Blocks. — Briefly  enumerated,  the 
following  advantages  are  claimed  for  concrete  blocks: 

1.  A    properly  constructed  concrete-block  wall  is  as  strong  or 
stronger  than  a  brick  wall  of  equal  thickness. 

2.  The  hollow  form  results  in  a  saving  of  materials  over  brick 
walls,  amounting  to  from  20  to  50  per  cent. 

3.  It  costs  less  to  build  a  concrete-block  wall  than  one  of  brick. 
This  is  due  to  the  much  larger  dimensions  of  the  concrete  block. 

4.  The  hollow  chambers  in  the  concrete  walls  tend  to  prevent 
moisture  from  penetrating  to  the  interior  face  of  the  wall;  lathing 
can  often,  therefore,  be  dispensed  with,  and  the  plastering  done 
directly  on  the  wall,  particularly  when  the  blocks  or  the  wall  has 
received  a  waterproofing  treatment. 

5.  The  hollow  chambers  form  an  air  cushion  that  prevents 
sudden  changes  of   temperature,  and  tends  to  keep   the  building 
cool  in  summer  and  easily  heated  in  winter. 

6.  The  fireproofing  qualities  of  concrete  blocks  are  superior  or 
at  least  equal  to  those  of  brick. 

7.  Pipes  and  wires  can  be  run  through  the  hollows  of  the  blocks, 
resulting  in  a  saving  of  space  and  labor  and  avoiding  ugly  appear- 
ances. 

8.  Concrete  blocks  can  be  manufactured  near  the  building  site. 
This  will  save  breakage,  also  part  of  the  cost  of  transportation  as 
compared  with  brick,  as  cement  in  bags  requires  less  handling  than 
brick. 

Materials  for  Concrete  Building  Blocks. — Building  blocks  are 
made  of  cement,  sand,  and  water  mixed  in  proper  proportions,  in 
which  case  they  are  properly  called  " mortar"  blocks;  or,  the 
above  materials  can  be  combined  with  either  broken  stone,  gravel, 
or  cinders,  in  which  cases  a  concrete  block  is  produced. 

Sand  and  gravel  will  usually  be  found  the  cheapest  and  most 
available  materials  to  employ. 

Since  the  space  for  concrete  in  the  mould  is  very  small,  the  block- 
builder  is  limited  to  the  use  of  gravel  and  stone  not  exceeding  1/2 
to  3/4  inch  in  size,  A  I  :  5  mixture  containing  such  gravel  or  screen- 


Handbook  for  Cement  and  Concrete  Users 

ings  will  produce  a  block  as  strong  and  as  durable  as  a  i  :  3  mixture 
with  sand  only. 

Cement. — Only  Portland  cement  should  be  used  in  the  manu- 
facture of  concrete  blocks,  as,  owing  to  its  present  cheapness, 
nothing  is  gained  by  using  substitutes.  Natural  and  slag  cements 
are  sometimes  used  for  blocks  that  are  supposed  to  remain  constantly 
wet,  but  such  blocks  rapidly  deteriorate  when  dry.  No  cement  is 
as  fully  reliable  as  Portland  cement,  and  only  the  latter  should  be 
considered  for  concrete  blocks. 

Broken  Stone.— This  should  be  small  enough  to  pass  through  a 
i -inch  mesh  screen.  If  there  is  much  dust  present  it  must  be 
removed  by  means  of  a  small  mesh  screen.  Another  way  is  to  wash 
out  the  dust.  A  barrel  having  a  wire-sieve  bottom  is  filled  with  the 
broken  stone,  and  water  is  run  through  the  stone;  the  water,  as  it 
runs  out,  will  carry  with  it  all  the  dust. 

Gravel. — If  gravel  is  used  it  should  be  screened  through  a  i-inch 
screen.  If  it  contains  much  clay  or  earth,  they  must  be  removed 
in  the  manner  described  for  broken  stone.  The  strength  of  the 
concrete  will  not  be  impaired  if  the  quantity  of  clay  and  earth 
present  does  not  exceed  3  per  cent. 

Cinders. — Cinders  are  sometimes  used  for  concrete  blocks  with 
fair  results.  Such  blocks  are  inferior  in  strength  to  those  made 
with  broken  stone  and  gravel  because  the  cinders  are  very  porous 
and  are  easily  crushed.  For  these  reasons  they  should  be  used  only 
where  great  strength  is  not  required;  for  instance,  in  interior  walls 
carrying  light  loads. 

Lime  is  sometimes  mixed  with  cement  mortar  to  improve  its 
qualities.  The  dry-slaked  or  hydrated  lime  is  the  most  convenient 
form  to  use,  and  it  is  mixed  in  the  proportion  of  one-quarter  to  one- 
half  of  the  cement  employed.  As  lime  is  about  as  expensive  as 
Portland  cement  there  is  no  saving  in  its  use.  It  will,  however, 
cause  the  blocks  to  set  more  rapidly,  will  make  them  lighter  in  color, 
and  the  concrete  will  be  denser  and  will  resist  better  the  penetration 
of  moisture. 

In  i  :  4  and  i  :  5  sand  mixtures  at  least  one-third  of  the  cement 
can  be  replaced  with  lime  without  appreciable  loss  of  strength. 

Proportion  of  Water. — The  quality  of  concrete  blocks  will. depend 
greatly  upon  the  amount  of  water  used.  A  dry  mixture  is  necessary 

[120 1 


Concrete  Building  Blocks 

if  the  block  is  to  be  removed  from  the  mould  as  soon  as  made.  Too 
much  water  will  cause  the  block  to  sag  out  of  shape,  should  the 
plates  be  removed  before  the  concrete  has  set. 

Processes  of  Manufacture. — There  are  two  ways  of  making 
concrete  blocks,  depending  upon  the  amount  of  water  used  in  the 
mixing.  These  are  called  the  "dry"  and  the  "wet"  processes. 

In  the  dry  process  just  enough  water  is  added  to  give  the  concrete 
the  consistency  of  damp  earth.  When  such  concrete  is  tamped  into 
a  block  machine,  the  mould  can  be  removed  immediately  after,  and 
the  process  continued. 

In  the  wet  process  sufficient  water  is  used  to  render  the  concrete 
mass  semi-fluid.  When  poured  into  the  moulds,  the  concrete  must, 
of  necessity,  remain  there  until  hardened. 

The  "wet"  process  produces  a  superior  block  both  in  point  of 
strength  and  waterproofing  qualities,  but  the  "dry"  process  is  by 
far  the  most  extensively  used. 

Blocks  made  of  too  dry  concrete  will  be  weak  and  will  crumble 
no  matter  what  process  of  curing  they  are  later  subjected  to.  It  is 
possible,  however,  to  obtain  a  mixture  with  enough  water  to  give 
the  required  density  and  hardening  qualities,  and  still  be  able  to 
remove  the  block  at  once  from  the  mould. 

It  is  impossible  to  give  a  fixed  percentage  of  the  amount  of  water 
required  as  this  varies  with  the  character  of  the  materials,  the 
moisture  in  the  atmosphere,  and  other  causes.  Generally  speaking, 
about  8  or  9  per  cent  of  the  weight  of  the  dry  mixture  will  be  found 
satisfactory. 

Types  of  Concrete  Blocks. — Concrete  blocks  may  be  classed 
under  two  headings : 

1.  One-piece  blocks  in  which  a  single  block  provided  with  one 
or  more  hollow  cores  makes  the  whole  thickness  of  the  wall. 

2.  Two-piece  blocks  in  which  the  face  and  back  of  the  wall  are 
made  up  of  different  pieces,  so  lapping  over  each  other  as  to  give 
a  bond  and  hold  the  wall  together. 

These  blocks  are  made  in  various  shapes  and  sizes,  the  standard 
size  having  the  following  dimensions: 

Length  32  inches,  height  9  inches,  and  thickness  8,  10,  and 
12  inches.  Blocks  are  also  made  with  lengths  of  24,  16,  and 
8  inches.  Because  of  the  excessive  weight  of  the  32-inch  block, 

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Handbook  for  Cement  and  Concrete  Users 

the  24-inch  size  is  rapidly  gaining  in  favor  among  architects  and 
builders. 

The  simplest  block  made  has  one  hollow  core  and  a  wall  erected 
with  such  blocks  will  have  a  series  of  vertical  air  spaces  running 
through  the  entire  height  of  the  wall. 

The  block  which  is  by  far  the  most  extensively  manufactured 
block  on  the  market,  is  reinforced  with  a  single  transverse  web,  thus 
giving  two  hollow  cores.  It  is  favored  not  so  much  because  of  its 
good  qualities  as  the  cheapness  of  manufacture.  This  block  is 
superior  to  the  single-core  block  in  point  of  strength.  It  has,  how- 


FIG.  31. — Concrete  Block  Having  Multiple  Air  Space. 

ever,  its  disadvantages.  The  transverse  webs  present  so  many 
additional  paths  for  moisture  to  penetrate  from  the  outer  wall  to 
the  inner.  The  tamping  of  concrete  around  two  cores  is  more 
difficult  than  around  one,  and  a  block  of  smaller  density  and  uni- 
formity is  produced.  Also,  a  block  with  two  cores  is  more  liable 
to  injury  in  the  process  of  removing  the  cores  than  a  block  with  one 
core. 

The  penetration  of  moisture  is  the  chief  defect  of  concrete  blocks, 
and  to  reduce  this  to  a  minimum  various  forms  have  been  evolved. 
Chief  among  these  are  blocks  with  staggered  air  spaces  and  the  two- 
piece  block. 

[  122! 


Concrete  Building  Blocks 

In  the  staggered  air  space  block,  known  as  the  Miracle  block, 
the  web  and  air  spaces  are  so  arranged  that  no  web  extends  directly 
from  the  outer  to  the  inner  wall.  The  air  spaces  register  exactly 
so  as  to  create  two  series  of  continuous,  perpendicular  air  chambers 
throughout,  all  solid  sections  being  backed  by  air  spaces.  This 
practically  assures  a  block  that  is  frost  and  moisture  proof. 

The  Blakeslee  block  is  another  type  of  block  having  a  width 
equal  to  the  whole  thickness  of  the  wall  in  which  there  is  no  direct 
connection  between  the  exterior  and  interior  walls.  Unlike  the 
Miracle  block,  however,  the  continuous  air  chambers  are  horizontal. 


FIG.  32. — Self  Lining  and  Interlocking  Concrete  Block. 

In  the  blocks  of  the  American  Hydraulic  Stone  Company,  each 
block  has  one  long  and  two  short  arms  which  break  joint  with  the 
corresponding  arms  of  the  adjacent  courses.  This  system  possesses 
many  advantages  over  other  systems  since  it  permits  a  continuity 
of  both  horizontal  and  vertical  air  spaces;  it  produces,  in  effect,  two 
walls,  thus  securing  thorough  insulation  and  making  a  concrete 
wall  construction  which  is  impenetrable  by  moisture. 

Two-piece  blocks  are  made  having  the  two  faces  tied  together 
with  galvanized  wire  during  the  process  of  manufacture,  making 
one  whole  block  to  handle  in  the  field. 

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Handbook  for  Cement  and  Concrete  Users 

Concrete  Block  Machines. — There  is  a  great  variety  of  concrete 
block  machines  on  the  market,  and  these  may  be  roughly  divided 
into  four  classes: 

1.  Machine  in  which  the  face  plate  is  vertical. 

2.  Machine  in  which  the  face  plate  is  horizontal. 

3.  Machine  for  pouring  blocks  from  wet  concrete. 

4.  Machine  for  making  blocks  of  the  two-piece  system. 
Machines  of  the  first  class  have  removable  hinged  sides,  and 

upright  interior  cores.      There  is  a  great  variety  of  labor-saving 


FIG.  33.— Hollow  Wall  of  Two-piece  Block. 

devices  to  be  found  in  the  different  machines,  but  the  principle  of 
manufacturing  the  blocks  is  essentially  the  same  in  all. 

The  blocks  are  made  by  tamping  under  the  "dry"  process  and 
immediately  removed  on  iron  pallets.  In  some  machines  the  labor 
needed  to  move  the  blocks  is  saved  by  turning  the  mould  over  and 
releasing  the  block  on  wood,  or  by  making  the  block  on  a  wooden 
board  and  lifting  the  mould  bodily  away  from  the  green  block. 
Several  types  of  machines  have  contrivances  for  mechanically  raising 
and  lowering  the  cores,  while  in  others  the  cores  remain  stationary, 
and  the  bottom  and  sides  are  adjustable. 

There  is  some  disadvantage  in  using  vertical-face  machines  when 
it  is  desired  to  make  a  block  with  facing  of  richer  concrete  than  is 
used  in  the  body  of  the  block.  Such  a  facing  is  often  desired  to 
secure  greater  impermeability  and  better  appearance.  It  is 

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Concrete  Building  Blocks 

necessary  then  to  provide  a  vertical  parting  plate,  and  great 
care  must  be  exercised  to  secure  an  intimate  bond  between  the 
two  mixtures;  otherwise,  the  facing  may  fall  off  in  rough  hand- 
ling or  with  the  freezing  of  moisture  which  may  settle  between 
the  two  mixtures. 

In  the  second  class  of  machines  the  face  plate  forms  the  bottom 
of  the  mould.  The  facing  mixture  is  first  deposited  and  tamped, 
after  which  the  cores  slide  in  laterally,  and  the  filling  and  tamping 
continued ;  the  mould  with  the  block  is  then  tipped  to  bring  the  face 
plate  to  a  vertical  position  and  the  block  removed. 

The  third  class  of  machines  for  making  blocks  from  very  wet 
concrete  consists  of  a  large  number  of  separable  moulds  made  from 
sheet  metal,  and  provided  with  interior  cores.  The  wet  concrete 
is  poured  into  the  moulds  and  allowed  to  harden  there  for  24 
hours.  The  principal  contentions  of  the  manufacturers  of  these 
moulds  are  that  the  blocks  possess  excellent  hardening  and 
waterproofing  qualities;  that  they  are  actual  stone,  and  are  cheaply 
made. 

Machines  of  the  fourth  class  differ  radically  from  all  other  types. 
This  is  due  to  the  fact  that  the  shape  of  the  "two-piece"  blocks  made 
on  these  machines,  permits  the  use  of  mechanical  and  hydraulic  press- 
ure. The  machines  are,  therefore,  of  heavy  and  complicated  con- 
struction, and  capable  of  large  output.  The  mixture  is  shovelled 
into  the  mould,  pressed  almost  instantaneously,  and  forthwith 
released.  Where  it  is  desired  to  have  a  facing  differing  in  color 
and  texture  from  the  body  of  the  block,  about  three-quar- 
ters of  an  inch  of  the  coarse  concrete  is  first  raked  out  before 
it  is  pressed,  the  facing  is  applied  to  this  loose  mass,  and  all 
pressed  at  one  time.  This  insures  a  firm  bond  between  the  face 
and  body  of  the  block,  and  as  the  pressure  is  applied  directly  to 
the  face  of  the  block,  a  beautiful  face  of  great  hardness  and  density 
is  produced. 

Making  the  Block. — Dry  Process. — The  concrete  should  be 
placed  in  the  mould  in  layers  about  3  inches  thick;  tamping  should 
begin  immediately  upon  the  placing  of  the  first  shovelful,  and  should 
be  continued  until  the  mould  is  full.  The  material  should  be  tamped 
with  a  tamper  having  a  small  face,  and  short,  quick,  sharp  blows 
should  be  struck. 


Handbook  for  Cement  and  Concrete  Users 

To  insure  a  block  of  the  same  consistency  throughout,  the 
tamping  must  be  very  thorough  and  should  be  continued  until 
water  appears  at  the  top.  This  will  insure  a  minimum  of  air  spaces 
and  voids. 

Wet  Process. — When  placing  the  material  in  the  mould,  the 
entire  mould  is  filled  with  one  pouring.  Of  late,  the  tamping  of 
concrete  by  means  of  mechanical  or  pneumatic  pressure  has  come 
into  extensive  use.  Moulding  concrete  by  pressure  is  not  successful 
unless  the  pressure  is  applied  to  the  face  of  a  comparatively  thin 
layer.  If  compression  of  thick  layers  is  attempted,  the  materials 
arch  and  are  not  compacted  at  any  considerable  depth  from  the 
surface.  Moulding  blocks  by  pressure  is  therefore  practical  only 
in  the  two-piece  system,  in  which  the  load  is  applied  to  the  surface 
of  pieces  having  no  great  thickness. 

Facing. — It  is  customary  now  to  use  for  the  facing  of  a  block 
a  richer  mixture  than  is  employed  for  the  body  of  the  block.  The 
following  are  the  advantages  of  facing: 

1.  Saving  in  Cost. — The  facing  being  not  more  than  1/2  inch 
thick,  there  is  a  considerable  saving  by  employing  a  coarser  material 
for  the  body  of  the  block. 

2.  A  dense  and  impervious  facing  is  secured  by  using  a  richer 
mixture  and  selected  aggregates. 

3.  A  pleasing  appearance  is  given  to  the  block.     This  may  be 
attained  by  introducing  a  coloring  mixture;    since  there  is  some 
danger  of  the  color  fading,  colored  sand  and  stone  may  be  used. 

It  is  of  the  utmost  importance  that  the  facing  and  the  rest  of 
the  block  be  thoroughly  bonded  together,  otherwise  there  is  danger 
of  a  cleavage  plane  being  formed.  The  manner  in  which  this 
may  be  accomplished  is  explained  under  the  heading  "Making  the 
Block." 

Concrete  blocks  being  moulded  from  a  plastic  material,  their 
faces  are  capable  of  endless  variations.  The  faces  most  commonly 
used  are  the  smooth  face,  panelled,  corrugated,  and  rock  faces,  also 
special  ornamental  designs.  In  choosing  a  facing  it  should  be  borne 
in  mind  that  a  concrete  block  possesses  ornamental  and  artistic 
properties  of  its  own,  and  a  far  more  pleasing  appearance  can  be 
obtained  by  bringing  these  out  than  by  imitating  other  kinds  of 
stone. 

[126] 


Concrete  Building  Blocks 

Curing. — The  curing  of  concrete  blocks  is  a  very  important 
consideration.  A  block  badly  cured  may  lose  all  the  good  qualities 
imparted  to  it  by  careful  manufacture. 

All  blocks  made  by  the  medium  wet  or  medium  dry  process, 
should  be  made  under  cover,  and  should  remain  on  the  pallet  at 
least  24  hours.  They  should  be  kept  under  cover  for  at  least  ten 
days,  protected  from  the  dry  currents  of  air.  Under  no  circum- 
stances should  blocks  be  made  under  the  direct  rays  of  the  sun, 
nor  should  blocks  be  exposed  either  to  sunshine  or  dry  winds 
while  curing. 

The  blocks  should  be  gently  sprinkled  as  soon  as  possible  after 
making;  that  is,  just  as  soon  as  the  cement  has  set  sufficiently  so 
that  it  will  not  wash. 

Plenty  of  water  is  absolutely  necessary.  The  process  of  harden- 
ing in  the  concrete  goes  on  for  a  great  many  days,  and  crystallization, 
upon  which  depends  the  strength  of  concrete,  cannot  go  on  without 
the  presence  of  a  sufficient  amount  of  water.  As  soon  as  a  block 
begins  to  turn  white,  it  is  a  sure  indication  that  water  is  lacking. 
Care  should  be  taken  to  so  pile  the  blocks  that  they  will  receive 
water  on  all  sides.  A  block  should  never  be  allowed  to  dry  out  on 
the  sides  before  the  centre  is  thoroughly  cured. 

Blocks  should  be  kept  wet  from  ten  days  to  two  weeks,  and 
should  never  be  removed  for  the  purpose  of  using  in  a  building  until 
they  are  from  thirty  to  sixty  days  old.  It  is  well  to  remember  that 
the  longer  a  block  is  cured,  the  harder  and  better  it  will  become. 

Coloring. — In  using  coloring  matter  with  concrete,  the  color 
should  always  be  mixed  with  the  cement  dry,  before  any  sand  or 
water  is  added.  The  mixing  should  be  thorough,  so  that  the 
mixture  is  uniform  in  color.  After  this  mixing,  the  combination 
is  treated  in  the  same  way  as  clear  cement. 

Pure  white  is  impossible  where  great  strength  and  durability 
are  required,  unless  white  Portland  cement  is  employed.  The 
following  formula  will  make  a  white  .block  which  is  stronger  than 
some  sandstones.  One  part  pulverized  lime,  or  hydrated  lime,  two 
parts  white  Portland  cement,  two  parts  pulverized  marble,  two  parts 
fine  washed  silica  sand,  two  parts  coarse  silica  sand. 

Blue-gray. — A  blue-gray  color  is  often  obtained  without  coloring 
matter  at  all,  by  using  a  blue  Portland  cement.  Light-colored 

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Handbook  for  Cement  and  Concrete  Users 

Portland  cement  may  be  blended  to  its  proper  color  by  the 
addition  of  seven  pounds  of  Ultramarine  blue  to  every  barrel  of 
cement. 

Gray. — Add  two  pounds  of  Germantown  lamp  black  to  every 
barrel  of  cement  used,  when  sand  is  of  light  color.  Dark  sand  will 
require  less.  Lampblack  is  a  protector  against  the  elements,  but 
reduces  the  strength  of  the  product;  not  enough,  however,  to  be 
detrimental  in  ordinary  dwelling-house  construction. 

Blue. — Add  from  ten  to  fifteen  pounds  of  Ultramarine  blue  to 
every  barrel  of  cement.  Use  dark-colored  cement. 

Black. — From  forty  to  fifty  pounds  of  Peroxide  of  Manganese 
to  each  barrel  of  cement. 

Red. — Twenty-five  pounds  of  Oxide  of  Iron  to  a  barrel  of 
cement. 

Bright  Red. — The  above  amount  of  English  Red  to  each  barrel 
of  cement. 

Lake  Superior  Red  Sandstone. — Twenty  pounds  Violet  Oxide 
of  Iron  to  a  barrel  of  cement.  Less  with  light  sand. 

Indiana  Bedford. — Ochres,  which  are  detrimental  to  the  stone 
by  reducing  its  strength,  must  be  used  for  making  buff  stone. 
Twelve  to  fifteen  pounds  of  Yellow  Ochre  to  every  barrel  of  cement 
will  produce  an  excellent  buff  stone. 

Waterproofing  Concrete  Blocks. — The  waterproofing  of  concrete 
has  been  treated  at  length  in  another  chapter;  it  is  well,  however, 
at  this  point,  to  enumerate  and  describe  the  various  methods  in 
so  far  as  they  are  applicable  for  securing  impermeability  of  concrete 
building  blocks. 

Concrete  blocks,  as  ordinarily  made,  are  exceedingly  porous 
and  readily  absorb  water;  this  is  especially  true  of  blocks  made  by 
the  "dry"  process.  This  tendency  to  absorb  water  gives  ground 
to  one  of  the  chief  objections  to  concrete  blocks.  Concrete  blocks, 
however,  are  no  more  water-absorbing  than  ordinary  bricks  and  it 
is  well  known  that  brick  walls  must  be  furred  and  lathed  to 
avoid  dampness;  but  concrete  block  walls  can  and  should  be 
sufficiently  waterproof  so  that  plastering  can  be  done  directly  on 
the  wall. 

The  different  methods  available  for  securing  impermeability 
in  concrete  blocks  are  as  follows: 


Concrete  Building  Blocks 

1.  Use  of  properly  graded  materials. 

2.  Use  of  rich  mixtures. 

3.  Use  of  a  facing. 

4.  Use  of  an  impervious  partition. 

5.  Use  of  waterproofing  compounds. 

6.  Applications  to  surface  after  erecting. 

All  the  above  methods  except  the  use  of  an  impervious  partition 
have  been  dwelt  upon  elsewhere  in  this  book.  Suffice  it  to  say  here 
that  the  use  of  a  waterproofing  compound  will  be  found  to  be  an 
effective  and  economical  method,  provided  the  compound  is  judi- 
ciously selected  and  the  work  done  conscientiously.  The  following 
explains  the  method  of  waterproofing  by  securing  an  impervious 
partition.  In  face-down  machines,  it  is  a  simple  matter,  after  the 
face  is  tamped  and  cores  pushed  into  place,  to  throw  into  each 
spacing  a  small  amount  of  rich  and  rather  wet  mortar,  spread  this 
evenly,  and  then  tamp  the  ordinary  mixture  until  the  mould  is  filled. 
A  dense  layer  across  each  of  the  cross-walls  is  thus  obtained,  which 
effectually  prevents  moisture  from  passing  beyond  it.  Recently  a 
method  was  patented  for  accomplishing  the  same  results  with 
vertical-face  machines.  Tapered  wooden  blocks  are  inserted  in 
the  middle  of  the  cross-walls.  After  tamping,  the  blocks  are  with- 
drawn, and  the  spaces  filled  with  rich  mortar. 

Building  Construction  Details. — It  is  usual  to  employ  the  follow- 
ing thicknesses  of  walls  in  concrete  block  construction: 

For  one-story  buildings 8  in.  walls 

For  two-story  buildings 10  in.  walls 

For  three-story  buildings 10  and  12  in.  walls 

For  four-story  buildings 10,  12,  and  15  in.  walls 

the  thickness,  of  course,  varying  from  the  foundation  upward. 

The  mortar  for  laying  concrete  blocks  should  be  composed  of 
i  part  of  Portland  cement  to  3  parts  of  sharp  sand.  It  is  well 
to  add  a  little  hydrated  lime  to  the  mortar  when  mixing.  This  will 
prevent  it  from  becoming  brittle. 

The  blocks  should  be  wet  when  set  in  the  wall,  otherwise  they 
will  absorb  moisture  from  the  mortar,  making  it  very  weak.  Point- 
ing should  be  done  the  same  way  as  in  laying  brick. 

Joists  can  be  fastened  by  cutting  into  the  blocks.  It  is  far 
preferable,  however,  to  use  hangers  for  this  purpose;  these  not 

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Handbook  for  Cement  and  Concrete  Users 

only  facilitate  construction,  but  possess  the  additional  merit  of 
distributing  the  load  on  the  joists  over  a  greater  section  of  the 
wall. 

Several  special  devices  are  employed  to  enable  one  to  lay  metal 
plugs  in  the  joists;  another  way  is  to  cast  a  wooden  plug  in  the 
concrete  when  moulding  the  block. 

Cost  of  Concrete  Blocks. — The  success  of  the  hollow  concrete 
block  industry  depends  to  a  great  extent  on  cheapness  of  product, 
since  it  is  necessary,  in  order  to  build  up  a  large  business,  to  compete 
in  price  with  common  brick  and  rubble  stone.  At  equal  cost, 
well-made  blocks  are  certain  to  be  preferred,  owing  to  their  super- 
iority in  strength,  convenience,  accurate  dimensions,  and  appearance. 
For  the  outside  walls  of  handsome  buildings,  blocks  come  into 
competition  with  pressed  brick  and  dressed  stone,  which  are,  of 
course,  far  more  costly.  Concrete  blocks  can  be  sold  and  laid  up 
at  a  good  profit  at  25  cents  per  cubic  foot  of  wall.  Common  red 
brick  costs  generally  about  12  dollars  per  thousand,  laid.  At  24 
to  the  cubic  foot,  a  thousand  brick  are  equal  to  41.7  cu.  ft.  of  wall; 
or,  at  $12,  2QC.  per  cu.  ft.  Brick  walls  with  pressed  brick  facing 
cost  from  4oc.  to  5oc.  per  cubic  foot,  and  dressed  stone  from 
$1.00  to  $1.50  per  foot. 

The  factory  cost  of  concrete  blocks  varies  according  to  the  cost 
of  materials.  Let  us  assume  cement  to  be  $1.50  per  barrel  of  380 
Ibs.,  and  sand  and  gravel  25c.  per  ton.  With  a  i  to  4  mixture,  i 
barrel  cement  will  make  1,900  Ibs.  of  solid  concrete,  or  at  130  Ibs. 
per  cu.  ft.,  14.6  cubic  feet.  The  cost  of  materials  will  then  be 

Cement,  380  Ibs $i .  50 

Sand  and  gravel,  1,5 20 Ibs o.  19 

Total  $i .  69 

or  n.5c.  per  cu.  ft.  solid  concrete.  Now,  blocks  9  inches  high  and 
32  inches  long  make  2  square  feet  of  face  of  wall,  each.  Blocks  of 
this  height  and  length,  8  inches  thick,  make  11-3  cubic  feet  of  wall; 
and  blocks  12  inches  thick  make  2  cubic  feet  of  wall.  From 
these  figures  we  may  calculate  the  cost  of  materials  for  these 
blocks,  with  cores  or  openings  equal  to  1/3  or  1/2  the  total  volume, 
as  follows: 


Concrete  Building  Blocks 

Per  cu.  ft.  of  block,  1-3  opening 7.7  cts. 

Per  cu.  ft.  of  block,  1-2  opening 5.8    " 

Block  8  X  9  X  32  inches,  1-3  opening 10.3    " 

Block  8X9X32  inches,  1-2  opening 7.7    " 

Block  12  X  9  X  32  inches,  1-3  opening 15.4    " 

Block  12  X  9  X  32  inches,  1-2  opening n.6    " 

If  one-third  of  the  cement  is  replaced  by  hydrated  lime  the 
quality  of  the  blocks  will  be  improved,  and  the  cost  of  material 
reduced  about  10  per  cent. 

The  cost  of  labor  required  in  manufacturing,  handling,  and 
delivering  blocks  will  vary  with  the  locality  and  the  size  and  equip- 
ment of  factory.  With  hand-mixing,  3  men  at  average  of  $1.75 
each  will  easily  make  75  8-inch  or  50  1 2-inch  blocks,  with  1-3 
openings,  per  day.  The  labor  cost  for  these  sizes  of  blocks  will 
therefore  be  7c.  and  10  i/2C.  respectively.  At  a  factory  equipped 
with  power  concrete  mixer  and  cars  for  transporting  blocks,  in 
which  a  number  of  machines  are  kept  busy,  the  labor  cost  will  be 
considerably  less.  An  extensive  industry  located  in  a  large  city  is, 
however,  subject  to  many  expenses  which  are  avoided  in  a  small 
country  plant,  such  as  high  wages,  management,  office  rent,  adver- 
tising, etc.,  so  that  the  total  cost  of  production  is  likely  to  be  about 
the  same  in  both  cases.  A  fair  estimate  of  total  factory  cost  is  as 
follows : 

Material.  Labor.            Total. 

8  X  32  inch,  J  space 10 .3  7  17.3  cts. 

8X32  inch,  \  "  7.7  6  13.7  " 

12  X  32  inch,  \  " 15 .4  10.5  25.9  " 

12  X  32  inch,  \  "  ii  .6  9  20.6  " 

With  fair  allowance  for  outside  expenses  and  profit,  8-inch 
blocks  may  be  sold  at  3oc.  and  1 2-inch  at  4oc.  each.  For  laying 
i2-inch  blocks  in  the  wall,  contractors  generally  figure  about  ice. 
each.  Adding  5c.  for  teaming,  the  blocks  will  cost  55c.  each,  erected, 
or  27  i/2c.  per  cubic  foot  of  wall.  This  is  less  than  the  cost  of 
common  brick,  and  the  above  figures  show  that  this  price  could  be 
shaded  somewhat,  if  necessary,  to  meet  competition. 

Objections  to  Concrete  Blocks  and  Remedies  for  Same. — In 
spite  of  the  admirable  qualities  of  concrete  blocks  as  a  building 
material,  their  use  has  not  been  so  extensive  as  their  merits  would 
seem  to  warrant.  There  is  still  considerable  opposition  from 
architects  and  builders  to  the  use  of  blocks.  This  is  not  due  to 


Handbook  for  Cement  and  Concrete  Users 

prejudice  against  the  new  material  concrete,  but  rather  to  the 
manner  in  which  this  material  is  used.  In  the  past  few  years,  a 
great  many  inexperienced  men  have  ventured  into  the  business  of 
block  manufacture,  allured  by  the  glowing  prospects  of  profit  held 
out  by  an  army  of  block-machine  agents.  As  a  result,  everywhere 
are  seen  glaring  examples  of  concrete-block  buildings  that  fall  far 
short  of  the  standard  of  excellence  that  is  claimed  can  be  attained. 

The  following  have  been  the  main  objections  to  the  use  of  con-, 
crete  blocks : 

Imitation  of  natural  stone. 

Poor  workmanship. 

Fixed  dimensions. 

Similarity  of  blocks. 

Too  great  weight. 

Unpleasing  appearance. 

Anything  that  savors  of  imitation,  that  pretends  to  be  what  it 
is  not,  will  be  shunned  by  right-minded  architects  and  builders. 
The  common  rock-faced  block  is  an  imitation  of  the  cheapest  form 
of  quarry  stone,  and  a  poor  imitation  at  that.  But  why  imitate 
granite  or  anything  else?  Why  not  bring  out  in  the  concrete  the 
beauty  that  is  peculiarly  its  own?  A  very  prominent  architect 
recently  said  in  a  conversation:  "These  block  makers  come  in 
here  and  say,  'Why  don't  you  use  blocks?  I  can  make  a  block 
that  ten  feet  away  you  can't  tell  from  red  sandstone  or  marble  or 
what  not.'  No,  I  don't  wish  a  concrete  block  that  I  can't  tell  from 
sandstone.  I  wish  a  concrete  block  that  won't  'flower.'  When  I 
wish  sandstone,  I  can  get  sandstone."  The  rebuke  is  just;  the 
concrete  block  maker  must  confine  his  energies  to  making  concrete 
blocks  and  not  to  imitating  sandstone. 

Poor  workmanship  can  be  eliminated  with  proper  inspection. 
Blocks  made  from  too  dry  mixtures  will  always  be  weak  and  will 
crumble,  and  can  easily  be  detected,  no  matter  how  much  they 
were  cured.  Good  concrete  produces  a  hard  and  dense  block  and 
emits  a  musical  tone  when  struck  with  a  hammer. 

Contractors  and  masons  often  object  to  the  size  of  the  block. 
A  12  x  32  inch  block  weighs  180  Ibs.,  and  to  hoist  a  number  of  these 
and  properly  handle  them  is  quite  a  task.  For  this  reason  the  use 
of  32-inch  blocks  is  decreasing,  except  for  large  buildings  and 


Concrete  Building  Blocks 

foundations;  and  the  24-inch  block  now  meets  with  most  favor. 
Such  a  block,  having  a  width  of  12  inches  and  a  height  of  9  inches, 
weighs  only  97  Ibs.,  and  if  properly  made,  possesses  sufficient 
strength  and  durability  to  meet  all  requirements. 

Concrete   Tiles   and   Other   Products.— There   are   now   being 
manufactured  on  a  large   scale,  concrete  wall  tiles,  shingles,  and 


FIG.  34. — Standard  Shapes  of  Concrete  Tile. 

other  accessories  for  building  construction.  While  the  machinery 
employed  varies  with  the  different  processes  employed  by  different 
makers,  the  general  principles  as  to  mixing,  curing,  etc.,  are  essen- 
tially the  same  as  in  ordinary  block-making. 


HOW  TO   FIGURE  THE   COST  OF   BLOCKS    (SEE    TABLE   XI) 

One  barrel  contains  3!  cubic  feet. 

One  cubic  yard  contains  7^  barrels. 

One  yard  of  sand  and  3!  bbls.  of  cement  equals  2  to  i  mixture. 

One  yard  of  sand  and  gravel  and  i^  bbls.  of  cement  equals  5  to  i  mixture. 

In  making  blocks  we  recommend  a  mixture  for  the  facing  of  one  part  cement,  2 
parts  coarse  sharp  clean  sand,  and  the  body  of  the  block,  i  part  cement,  2  parts  sand, 
and  three  parts  gravel  or  broken  stone.  The  gravel  or  broken  stone  to  range  in  size 
from  ¥  to  f "  in  diameter. 

For  manufacturing  100  blocks  8  x  8  x  16  inches  there  is  needed  2.24  barrels  of 
cement,  0.68  cubic  yards  of  sand,  and  1.06  cubic  yards  of  gravel  or  broken  stone  which, 
at  the  following  estimated  cost  of  materials,  will  amount  to: 


EXAMPLE 

2.24  barrels  of  best  Portland  cement  at  $2.00  per  bbl.  .  .  . 

0.68  cubic  yards  of  sand  at  $1.00  cu.  yd 

i. 06  cubic  yards  of  gravel  or  broken  stone  at  $1.50  cu.  yd. 

Cost  for  labor  for  100  blocks 

Incidentals  for  safe  margin  per  100  blocks 


Total  cost  for  100  blocks  8  x  8  x  16" 


$4-48 
.68 


-5° 
$9.00 


The  above  are  approximate  and  conservative  prices  for  materials  and  labor.  These 
may  vary,  however,  to  a  less  or  higher  degree  governed  by  locality. 

The  cost  of  concrete  blocks  in  any  locality  will  be  found  to  be  much  less  than  that  of 
common  brick  and  they  are  also  a  better  and  more  lasting  material. 

[133] 


Handbook  for  Cement  and  Concrete  Users 


TABLE  XI.— CONCRETE  BLOCK  DATA.* 

Giving  size  and  weight  of  blocks,  the  number  one  barrel  of  cement  will  make, 
the  number  to  one  cubic  yard  of  material  and  the  number  per  square  of  one 
hundred  superficial  feet. 


5^5 

§  £  g1 

&  5  3 

SOLID  BLOCKS. 

HOLLOW  BLOCKS. 

No.  per 
Square  of 

100 

Square 
Feet. 

Weight  of 
Block. 
Pounds. 

No.  per 
Bbl.  of 
Cement 
at  i  to  5. 

No.  per 
Cubic 
Yard. 

Weight 
of  Block. 
Pounds. 

No.  per 
Bbl.  of 
Cement 
at  i  to  5. 

No.  per 
Cubic 
Yard. 

8  X  8  X  16 

73 

34 

48 

5° 

49 

71 

IT2 

8  X  10  X  16 

92 

27 

38 

67 

37 

53 

112 

8  X  12  X  16 

109 

22 

32 

80 

3i 

44 

112 

4  X  8  X  16 

35 

68 

99 

24 

100 

144 

224 

4  X  10  X  16 

44 

54 

79 

32 

76 

109 

2J4 

4  X  12  X  16 

53 

44 

66 

39 

63 

91 

224 

8  X  4  X  16 

37 

68 

95 

112 

8  X  8  X  24 

112 

22 

3i 

77 

32 

45 

75 

8  X  10  X  24 

140 

18 

25 

92 

25 

38 

75 

8  X  12  X  24 

1  66 

15 

21 

112 

21 

31 

75 

4  X  8  X  24 

54 

46 

65 

37 

66 

94 

15° 

4  X  10  X  24 

67 

36 

5  2 

46 

52 

76 

i$° 

4  X  12  X  24 

79 

3° 

44 

55 

44 

63 

150 

8  X  4  X  24 

55 

44 

63 

75 

EXPLANATION. — To  find  the  number  of  blocks  for  a  building,  get  the  surface  feet  of 
the  building  by  multiplying  the  length  around  the  building  by  the  height  of  the  wall. 
Add  to  this  the  surface  of  gables,  then  deduct  the  surface  feet  of  all  the  openings,  thus 
giving  the  actual  surface  to  cover. 

Rule. — Multiply  the  number  of  squares  to  cover  by  the  number  in  the  last  column, 
for  the  size  block  you  are  to  use,  which  will  give  the  number  of  blocks  for  any  building. 


*  Published  by  the  Ideal  Concrete  Machinery  Company. 

[134] 


Concrete  Building  Blocks 


STANDARD   SPECIFICATIONS   FOR   CONCRETE   BLOCKS 

RULES  AND  REGULATIONS  FOR  BLOCKMAKERS,  AS  REVISED,  CORRECTED,  AND  ADOPTED 
BY  THE  NATIONAL  ASSOCIATION  OF  CEMENT  USERS  AT  THEIR  CONVENTION,  1908. 

Concrete  hollow  blocks  made  in  accordance  with  the  following  specifications, 
and  meeting  the  requirements  thereof,  may  be  used  in  building  construction,  subject 
to  the  usual  form  of  approval  required  of  other  materials  of  construction  by  the  Bureau 
of  Building  Inspection: 

1.  Cement. — The  cement  used  in  making  sand  blocks  shall  be  Portland  cement, 
capable  of  passing  the  requirements  as  set  forth  in  the  "Standard  Specifications  for 
Cement,"  by  the  American  Society  for  Testing  Materials. 

2.  Sand. — The  sand  used  shall  be  suitable  silicious  material,  passing  the  one -fourth- 
inch  mesh  sieve,  clean,  gritting,  and  free  from  impurities. 

3.  Stone  or  Coarse  Aggregate. — This  material  shall  be  clean  broken  stone,  free  from 
dust,  or  clean  screened  gravel  passing  the  three-quarter  (f)  inch,  and  refused  by  the 
one-quarter  (^)  inch,  mesh  sieve. 

4.  Unit  of  Measurement. — The  barrel  of  Portland  cement  shall  weigh  380  pounds 
net,  either  in  barrels  or  sub-divisions  thereof,  made  up  of  cloth  or  paper  bags,  and  a 
cubic  foot  of  cement  shall  be  called  not  to  exceed  100  pounds  or  the  equivalent  of  3.8 
cubic  feet  per  barrel.     Cement  shall  be  gauged  or  measured  either  in  the  original 
package  as  received  from  the  manufacturer,  or  may  be  weighed  and  so  proportioned; 
but  under  no  circumstances  shall  it  be  measured  loose  in  bulk. 

5.  Proportions.  For  exposed  exterior  or  bearing  walls:   (a)  Concrete  hollow  blocks, 
machine-made,  using  semi-wet  concrete  or  mortar,  shall  contain  one  (i)  part  cement, 
not  to  exceed  three  (3)  parts  sand,  and  not  to  exceed  four  (4)  parts  stone,  of  the  character 
and  size  before  stipulated.     When  the  stone  shall  be  omitted,  the  proportions  of  sand 
shall  not  be  increased,  unless  it  can  be  demonstrated  that  the  percentage  of  voids  and 
tests  of  absorption  and  strength,  allow  in  each  case  of  greater  proportions,  with  equally 
good  results,     (b)  When  said  blocks  are  made  of  slush  concrete,  in  individual  moulds, 
and  allowed  to  harden  undisturbed  in  same  before  removal,  the  proportions  may  be 
one  (i)  part  cement  to  not  exceed  three  (3)  parts  sand  and  five  (5)  parts  stone,  but  in 
this  case  also,  if  the  stone  be  omitted,  the  proportions  of  sand  shall  not  be  increased. 

6.  Mixing. — Thorough  and  vigorous  mixing  is  of  the  utmost  importance. 

(a)  Hand  Mixing. — The  cement  and  sand  in  correct  proportions  shall  be  first 
perfectly  mixed  dry,  the  water  shall  then  be  added  carefully  and  slowly  in  proper  pro- 
portions, and  thoroughly  worked  into  and  throughout  the  resultant  mortar;  the  moist- 
ened gravel  or  broken  stone  shall  then  be  added,  either  by  spreading  same  uniformly 
over  the  mortar,  or  spreading  the  mortar  uniformly  over  the  stones,  and  then  the 
whole  mass  shall  be  vigorously  mixed  together  until  the  coarse  aggregate  is  thoroughly 
incorporated  with  and  distributed  throughout  the  mortar. 

(b)  Mechanical  Mixing. — Preference  shall  be  given  to  mechanical  mixers  of  suitable 
design  and  adapted  to  the  particular  work  required  of  them;    the  sand  and  cement, 
or  sand  and  cement  and  moistened  stone  shall,  however,  be  first  thoroughly  mixed 
before  the  addition  of  water,  and  then  continued  until  the  water  is  uniformly  dis- 
tributed or  incorporated  with  the  mortar  or  concrete  (such  as  will  quake  or  flow).  This 
procedure  may  be  varied  with  the  consent  of  the  Bureau  of  Building  Inspection,  archi- 
tect, or  engineer  in  charge. 

7.  Moulding.— Due  care  shall  be  used  to  secure  density  and  uniformity  in  the 
blocks  by  tamping  or  other  suitable  means  of  compression.     Tamped  blocks  shall  not 


Handbook  for  Gement  and  Concrete  Users 

be  finished  by  simply  striking  off  with  a  straight  edge,  but,  after  striking  off,  the  top  sur- 
faces shall  be  trowelled  or  otherwise  finished  to  secure  density  and  a  sharp  and  true  arris. 

8.  Curing. — Every  precaution  shall  be  taken  to  prevent  the  drying  out  of  the  blocks 
during  their  initial  set  and  first  hardening.     A  sufficiency  of  water  shall  first  be  used 
in  the  mixing  to  perfect  the  crystallization  of  the  cement,  and,  after  moulding,  the  block 
shall  be  carefully  protected  from  wind  currents,  sunlight,  dry  heat,  or  freezing,  for  at 
least  five  (5)  days,  during  which  time  additional  moisture  shall  be  supplied  by  approved 
methods,  and  occasionally  thereafter  until  ready  for  use. 

9.  Ageing. — Concrete  hollow  blocks  in  which  the  ratio  of    cement  to    sand  be 
one-third  (§)  (one  part    cement  to    three  parts  sand),  shall  not  be  used   in  the  con- 
struction of  any  building  in  the  (City)  of ,  (Town)  of , 

until  they  have  attained  the  age  of  not  less  than  three  (3)  weeks. 

Concrete  hollow  blocks  in  which  the  ratio  of  cement  to  sand  be  one-half  (2)  (one 
part  cement  to  two  parts  sand),  may  be  used  in  construction  at  the  age  of  two  (2)  weeks, 
with  the  special  consent  of  the  Bureau  of  Building  Inspection,  and  the  architect  or 
engineer  in  charge. 

Special  blocks  of  rich  composition,  required  for  closures,  may  be  used  at  the  age  of 
seven  (7)  days  with  the  special  consent  of  same  authorities. 

The  time  herein  named  is  conditional,  however,  upon  maintaining  proper  con- 
ditions of  exposure  during  the  curing  period. 

10.  Marking. — All  concrete  blocks  shall  be  marked  for  purposes  of  identification, 
showing  name  of  manufacturer  or  brand,  date  (day,  month,  and    year)  made,  and 
composition   or  proportions  used;  as,  for  example,  1:3:5,  meaning  one  cement,  three 
sand,  and  five  stone. 

n.  Thickness  of  Watts. — The  thickness  of  bearing  walls  for  any  building  where 
concrete  hollow  blocks  are  used,  may  be  ten  (10)  per  cent  less  than  is  required  by  law 
for  brick  walls.  For  curtain  walls,  or  partition  walls,  the  requirements  shall  be  the 
same  as  in  the  use  of  hollow  tile,  terra-cotta,  or  plaster  blocks. 

12.  Party  Watts. — Hollow  concrete  blocks  shall  not  be  permitted  in  the  construction 
of  party  walls,  except  when  filled  solid. 

13.  Walls,  Laying  Of. — Where  the  face  only  is  of  hollow  concrete  block,  and   the 
backing  is  of  brick,  the  facing  of  hollow  block  must  be  strongly  bonded  to  the  brick 
either  with  headers  projecting  four  (4)  inches  into  the  brickwork,  every  fourth  course 
being  a  heading  course,  or  with  approved  ties;  no  brick  backing  to  be  less  than  eight 
(8)  inches.     Where  the  walls  are  made  entirely  of  concrete  blocks,  but  where  said 
blocks  have  not  the  same  width  as  the  wall,  every  fifth  course  shall  extend  through  the 
wall,  forming  a  secure  bond,  when  not  otherwise  sufficiently  bonded.     All  walls,  where 
blocks  are  used,  shall  be  laid  up  with  Portland  cement  mortar. 

14.  Girders  or  'Joists. — Wherever  girders  or  joists  rest  upon  walls  so  that  there  is 
a  concentrated  load  on  the  block  of  over  two  (2)  tons,  the  block  supporting  the  girder 
or  joists  must  be  made  solid  for  at  least  eight  (8)  inches  from  the  inside  face.     Where 
such  concentrated  load  shall  exceed  five  (5)  tons,  the  blocks  for  at  least  three  courses 
below,  and  for  a  distance  extending  at  least  eighteen  (18)  inches,  each  side  of  said 
girder  shall  be  made  solid  for  at  least  eight  (8)  inches  from  the  inside  surface.     Wherever 
walls  are  decreased  in  thickness,  the  top  course  of  the  thicker  wall  shall  afford  a  full 
solid  bearing  for  the  webs  or  walls  of  the  course  of  blocks  above. 

15.  Limit  of  Loading. — No  wall,  nor  any  part  thereof,  composed  of  concrete  hollow 
blocks,  shall  be  loaded  to  an  excess  of  eight  (8)  tons  per  superficial  foot  of  the  area  of 
such  blocks,  including  the  weight  of  the  wall,  and  no  blocks  shall  be  used  in  bearing 


Concrete  Building  Blocks 


walls  that  have  an  average  crushing  at  less  than  1,000  pounds  per  sq.  in.  of  area,  at 
the  age  of  twenty-eight  (28)  days;  no  deduction  to  be  made  in  figuring  the  area  for  the 
hollow  spaces. 

1 6.  Sills  and  Lintels. — Concrete  sills  and  lintels  shall  be  reinforced  by  iron  or  steel 
rods  in  a  manner  satisfactory  to  the  Bureau  of  Building  Inspection,  and  the  architect 
or  engineer  in  charge,  and  any  lintels  spanning  over  four  feet  six  inches  shall  rest  on 
block  solid  for  at  least  eight  inches  from  the  face  next  the  opening  and  for  at  least  three 
courses  below  the  bottom  of  the  lintel. 

17.  Hollow  Space. — The  hollow  space  in  building  blocks,  used  in  bearing  walls, 
shall  not  exceed  the  percentage  given  in  the  following  table  for  different  height  walls, 
and  in  no  case  shall  the  walls  or  webs  of  the  block  be  less  in  thickness  than  one-fourth 
their  height.     The  figures  given  in  the  table  represent  the  percentage  of  such  hollow 
space  for  different  height  walls. 

TABLE  XII.— HOLLOW  SPACES  IN  BLOCKS. 


Stories. 

ist. 

2nd. 

3rd. 

4th. 

sth. 

6th. 

i  and  2  

33 

33 

3  and  4  

25 

33 

33 

33 

5  and  6  

20 

25 

25 

33 

33 

33 

1 8.  Application  for  Use. — Before  any  such  material  be  used  in  buildings,  an  applica- 
tion for  its  use  and  for  a  test  of  the  same  must  be  filed  with  the  Bureau  of  Building 
Inspection.     In  the  absence  of  such    a  bureau  the  application  shall  be  filed  with  the 
chief  of  any  department  having  such  matters  in  charge.     A  description  of  the  material 
and  a  brief  outline  of  its  manufacture  and  proportions  used  must  be  embodied  in  the 
application.     The  name  of  the  firm  or  corporation,  and  the  responsible  officers  thereof, 
shall  also  be  given,  and  changes  in  same  thereafter  promptly  reported. 

19.  Preliminary  Test. — No  hollow  concrete  blocks  shall  be  used  in  the  construction 
of  any  building  unless  the  maker  of  said  blocks  has  submitted  his  product  to  the  full 
tests  required  herein,  and  placed  on  file  with  the  Bureau  of  Building  Inspection,  or 
other  duly  authorized  official,  a  certificate  from  a  reliable  testing  laboratory,  showing 
that  representative  samples  have  been  tested  and  successfully  passed  all  requirements 
thereof,  and  giving  in  detail  the  results  of  the  tests  made. 

No  concrete  blocks  shall  be  used  in  the  construction  of  any  building  until  they  have 
been  inspected  and  approved,  or,  if  required,  until  representative  samples  be  tested  and 
found  satisfactory.  The  results  of  all  tests  made,  whether  satisfactory  or  not,  shall  be 
placed  on  file  in  the  Bureau  of  Building  Inspection.  These  records  shall  be  open  to 
inspection  upon  application,  but  need  not  necessarily  be  published. 

20.  Additional  Tests. — The  manufacturer  and  user  of  such  hollow  concrete  blocks, 
or  either  of  them,  shall,  at  any  and  all  times,  have  made  such  tests  of  the  cement  used 
in  making  such  blocks,  or  such  further  tests  of  the  completed  blocks,  or  of  each  of 
these,  at  their  own  expense,  and  under  the  supervision  of  the  Bureau  of  Building  In- 
spection, as  the  chief  of  said  bureau  shall  require. 

In  case  the  result  of  tests  made  under  this  condition  should  show  that  the  standard 
of  these  regulations  is  not  maintained,  the  certificate  of  approval  issued  to  the  manu- 
facturer of  said  blocks  will  at  once  be  suspended  or  revoked. 

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Handbook  for  Cement  and  Concrete  Users 

21.  Certificate  of  Approval. — Following  the  application  called  for  in  clause  No.  18, 
and  upon  the  satisfactory  conclusion  of  the  tests  called  for,  a  certificate  of  approval 
shall  be  issued  to  the  maker  of  the  blocks  by  the  Bureau  of  Building  Inspection.     This 
certificate  of  approval  will  not  remain  in  force  for  more  than  four  months,  unless  there 
be  filed  with  the  Bureau  of  Building  Inspection,  at  least  once  every  four  months  fol- 
lowing, a  certificate  from  some  reliable  physical  testing  laboratory  showing  that  the 
average  of  at  least  three  (3)  specimens  tested  for  transverse  strength,  comply  with  the 
requirements  herein  set  forth.     The  said  samples  to    be   selected  by   a  building  in- 
spector, or  by  the  laboratory,  from  blocks  actually  going  into  constructing  work. 

22.  Test  Requirements. — Concrete  hollow  blocks  must  be  subjected  to  the  following 
tests:     Transverse,  compression,  and  absorption,  and  may  be  subjected  to  the  freezing 
and  fire  tests,  but  the  expense  of  conducting  the  freezing  and  fire  tests  will  not  be  im- 
posed upon  the  manufacturer  of  said  blocks. 

The  test  samples  must  represent  the  ordinary  commercial  product,  of  the  regular 
size  and  shape  used  in  construction.  The  samples  may  be  tested  as  soon  as  desired 
by  the  applicant,  but  in  no  case  later  than  sixty  days  after  manufacture. 

Transverse  Test. — The  modulus  of  rupture  for  concrete  blocks  at  28  days  must 
average  one  hundred  and  fifty,  and  must  not  fall  below  one  hundred  in  any  case. 

Compression  Test. — The  ultimate  compressive  strength  at  28  days  must  average 
one  thousand  (1,000)  pounds  per  square  inch,  and  must  not  fall  below  seven  hundred 
in  any  case. 

Absorption  Test. — The  percentage  of  absorption  (being  the  weight  of  water  ab- 
sorbed, divided  by  the  weight  of  the  dry  sample)  must  not  average  higher  than  15  per 
cent,  and  must  not  exceed  22  per  cent  in  any  case. 

23.  Condemned  Block. — Any  and  all  blocks,  samples  of  which  on  being  tested  under 
the  direction  of  the  Bureau  of  Building  Inspection,  fail  to  stand  at  twenty-eight  (28) 
days  the  tests  required  by  this  regulation,  shall  be  marked  condemned  by  the  manu- 
facturer or  user  and  shall  be  destroyed. 

24.  Cement  Brick. — Cement  brick  may  be  used  as  a  substitute  for   clay  brick. 
They  shall  be  made  of  one  part  cement  to  not  exceeding  four  parts  clean  sharp  sand, 
or  one  part  cement  to  not  exceeding  three  parts  clean  sharp  sand  and  three  parts  broken 
stone  or  gravel  passing  the  one-half  inch  and  refused  by  the  one-quarter  inch  mesh 
sieve.     In  all  other  respects  cement  brick  must  conform  to  the  requirements  of  the 
foregoing  specifications. 


CHAPTER  XIV 

THE  MAKING  OF  ORNAMENTAL  CONCRETE 

Methods  Employed. — Modelling. — Moulding. — Wooden,  Metal,  Plaster,  Glue,  and 

Sand  Moulds. 

ORNAMENTAL  concrete,  as  has  already  been  referred  to  in  the 
section  on  Concrete  Architecture  (under  which  this  chapter  might 
also  have  been  included),  is  now  playing  a  large  part,  and  is  des- 
tined to  play  a  still  greater  part  in  enhancing  the  elegance  and 
beauty  of  our  modern  homes,  gardens,  and  landscapes. 

The  development  of  the  various  methods  of  manufacture  has 
given  us  the  possibility  of  the  highest,  as  well  as  the  most  enduring, 
architectural  effects,  and  most  of  these  are  within  the  financial  reach 
of  the  most  modest  home.  Simple  pottery,  garden  furniture,  and 
other  handsome  decorative  work  can  be  made  at  home  by  the 
exercise  of  care,  patience,  and  some  study  and  the  possible  enhance- 
ment of  any  home  in  appearance  by  their  use  cannot  be  over- 
estimated. The  principal  methods  of  making  these  products  are 
given  in  the  following  pages. 

All  the  precautions  to  be  observed  in  ordinary  concrete  work 
are  especially  important  in  ornamental  work.  The  sand  must  be 
clean  and  free  from  loam,  or  the  ornament  will  have  a  dirty  color, 
and  if  any  color  work  is  to  be  attempted  either  with  pigments  or 
colored  stones,  cleanliness  of  sand  is  absolutely  necessary.  Sound- 
ness of  cement  is  important  because  sharp  edges  will  crumble  if 
the  cement  is  not  sound.  The  aggregate,  too,  must  be  selected  to 
produce  the  desired  effect.  Ordinary  concrete  is  dull  and  monoto- 
nous, and  this  must  be  remedied  in  ornamental  work  by  using  selected 
aggregate,  either  marble  dust  and  small  marble  chips  to  produce  a 
white  effect,  or  selected  red,  brown,  or  blue  stones  for  color  effects. 
The  color  and  sparkle  of  the  stones  must  be  brought  out  by  surface 
treatment  as  explained  in  Chapter  XII. 

Methods  of  Manufacture. — The  methods  of  making  concrete 
ornaments  and  producing  ornamental  effects  in  concrete  can  be 

[i39] 


Handbook  for  Cement  and  Concrete  Users 


divided  into  two  general  classes:  first,  modelling,  which  includes  all 
concrete  work  built  without  moulds,  usually  onto  wire  mesh  founda- 
tions and  modelled  into  shape  by  hand  or  by  scraping  with  templets 
of  wood  or  metal;  and  second,  moulding  which  includes  all  concrete 
work  made  in  forms. 

Modelling. — The  cheapest  and  quickest  way  to  make  simple 
designs  where  only  one  or  two  of  a  kind  are  planned  is  that  of 
modelling.  It  is  surprising  how  great  a  variety  of  forms  can  be 


FIG.  35. — Wire -mesh  Frames  for  Modelling  Concrete  Pottery. 


CIRCULAR 

WOOD  FORM, 

•     __^M 


COVfRCO 
WIRE    FRAM6 


FIG.  36. — How  Rough-Coated  Jar  is  Attached  to  Circular  Wood  Form. 

obtained  by  a  little  ingenuity.  The  fundamental  principle  in  every 
,  case,  no  matter  how  simple  or  complicated,  is  to  make  a  skeleton 
of  wire  mesh,  or  some  rough  material,  or  build  up  the  body  solid, 
approximately  the  form  of  the  finished  product,  and  lay  onto  this 
rough  body  the  concrete  to  the  proper  lines.  Then  finish  with  a 
templet  by  revolving  the  concreted  form  about  its  centre,  the  templet 
being  held  still.  We  will  describe  a  simple  case  from  which  the 
reader  will  be  able  to  see  the  method  and  easily  make  more  com- 
plicated designs. 

[140] 


The  Making  of  Ornamental  Concrete 

To  make  a  cylindrical  vase  by  modelling,  procure  sufficient  wire 
mesh,  and  with  a  compass  or  piece  of  string  and  chalk,  describe  a 
circle  on  the  mesh  about  the  size  of  the  base  of  the  vase  to  be  made. 
With  a  pair  of  wire-cutters,  cut  the  mesh  at  each  point  on  the  circle. 
Now  cut  a  rectangular  piece  an  inch  and  a  half  longer  than  the 
circumference  of  the  circle  just  made,  and  an  inch  broader  than  the 
height  of  the  vase.  Roll  this  piece  on  a  table  or  board  into  a  cylinder 
the  size  of  the  vase;  the  extra  inch  and  one-half  will  overlap.  This 
is  to  hold  the  cylinder  fast.  Lay  this  on  the  table  and  place  the 
bottom  on  top  of  it,  and  bend  the  wires  of  the  sides  around  the 
bottom.  This  makes  a  firm  and  tight  cage  on  which  to  build  your 
ornament.  Now  mix  up  sufficient  concrete  for  the  scratch  coat  and 
with  a  small  trowel  or  knife  force  this  into  the  mesh,  leaving  the 
outside  rough  as  possible  so  as  to  form  a  bond  with  the  finishing 
coat.  Cut  an  inch  board  into  a  circle  a  little  larger  than  the  frame, 
equal  to  the  outside  diameter  of  the  ornament  and  in  the  centre  of  the 
board  drive  a  nail ;  place  the  unfinished  piece  on  this  board  with  the 
projecting  nail  in  its  centre  so  that  when  the  piece  is  revolved  about 
this  nail,  every  point  of  the  frame  will  be  an  equal  distance  from 
the  circumference  of  the  board.  Now  make  a  scraping  tool  by 
attaching  two  pieces  of  inch  wood  together  to  form  right  angles 
and  bevel  the  edge  of  one  to  form  a  cutting  edge.  Next  mix  your 
finishing  coat  and  apply  as  before  with  a  small  trowel  when  the 
concrete  is  built  out  to  the  circular  base.  Take  your  scraping 
tool  and  hold  it  on  a  table  or  board  so  that  the  cutting  edge  is 
vertical  and  rests  tight  against  the  wooden  base.  Revolve  the 
base  board  and  concreted  frame  together;  the  tool  will  scrape  off 
the  projections.  Fill  in  all  holes  with  more  concrete  and  continue 
revolving  until  the  cutting  edge  touches  at  every  point  and  there 
are  no  projections.  Next  level  off  the  top  to  the  right  height  by 
similar  method,  having  the  tool  fixed  at  proper  height  and  revolving 
your  piece  until  a  smooth  surface  is  procured.  The  inside  is  built 
out  to  the  desired  thickness  and  finished  by  scraping  and  filling 
until  its  surface  is  parallel  to  the  outside  surface.  This  can  best 
be  done  by  using  three  pieces  of  wood  formed  into  a  U,  the  distance 
between  the  two  vertical  legs  being  the  thickness  of  the  piece 
and  their  lengths  equal  to  the  height  of  the  piece.  The  inside 
should  not  be  started  until  after  the  outer  coat  has  set  for  about 

[141] 


Handbook  for  Cement  and  Concrete  Users 

6  to  12  hours;  it  will  then  be  sufficiently  hard  so  that  the  tool 
will  not  injure  its  surface.  The  inside  bottom  is  finished  by  hold- 
ing a  board  about  as  wide  as  the  inside  diameter  and  revolving  the 
ornament  as  before. 

A  small  amount  of  goats'  hair  added  to  the  concrete  makes  it 
hold  together  and  the  concrete  should  not  be  mixed  very  wet. 

No  matter  how  complicated  the  form  is,  the  method  is  essentially 
the  same,  a  cutting  edge  being  used  to  form  a  guide,  usually  of  wood, 
on  which  the  ornament  rests  and  is  centered.  If  the  ornament  is 
square  or  oblong,  the  cutting  edge  is  moved  along  each  side  of  the 
piece  of  wood  until  all  are  formed. 

If  the  form  has  a  spherical  surface,  a  templet  of  a  circular  shape 
must  be  cut  to  scrape  to  the  right  lines. 

This  method  of  scraping  is  often  used  to  form  solid  mould- 
ings, copings,  etc.,  the  ornament  being  built  in  place  by  moulds 
and  the  top  built  up  and  scraped  to  the  desired  lines  by  temp- 
lets formed  of  sheet  iron  backed  with  lumber.  The  templet  is 
moved  along  the  top  edge  of  the  form.  The  ornaments  made  in 
this  way  can  be  further  decorated  by  one  or  other  of  the  ways  to 
be  described  later. 

Moulding. — The  method  of  making  concrete  ornaments  most 
generally  in  use  and  the  one  most  economical  and  satisfactory  where 
any  number  of  a  similar  form  are  to  be  made,  is  that  of  moulding. 
There  are  many  different  methods  of  moulding,  and  each  is  especially 
adapted  to  special  classes  of  work.  The  simplest,  perhaps,  is  the 
wooden  mould,  where  the  object  to  be  formed  is  composed  of  straight 
lines  such  as  square  or  oblong  boxes  decorated  with  diamonds  or 
some  such  simple  impression,  or  ornamental  concrete  lattice  work 
for  porches,  fences,  etc.  When  the  forms  become  more  complicated, 
standard  plaster,  sand,  or  glue  moulds  must  be  employed. 

Standard  moulds  are  best  wherever  ornaments  are  to  be  made 
on  a  commercial  scale  large  enough  to  warrant  their  first  cost,  and 
when  they  can  be  procured  of  proper  size  and  form  for  the  purpose. 
As  ornamental  concrete  work  is  in  its  infancy,  the  variety  of  standard 
forms  on  the  market  at  present  is  not  very  large,  and  it  is  much 
better  to  make  a  form  for  yourself  than  to  accept  one  that  does  not 
fill  your  requirements.  With  present  progress,  there  is  no  doubt 
that  in  a  very  short  time  there  will  be  such  a  variety  of  forms  that 


The  Making  of  Ornamental  Concrete 

it  will  be  absurdly  extravagant  to  make  one  for  yourself,  unless 
your  need  is  unique. 

Wooden  Moulds. — In  making  ornaments  with  wooden  forms 
or  moulds,  all  that  is  necessary  is  to  build  an  outside  mould  of 
such  form  that  its  inside  corresponds  to  the  outside  of  desired  orna- 
ment; if  your  ornament  is  to  be  hollow  or  have  an  open  bowl, 
make  a  core  or  inside  mould,  the  outside  of  the  core  corresponding 
to  the  inside  of  the  ornament.  The  core  must  be  in  so  many  parts 
that  it  can  be  removed  without  injuring  the  ornament  after  it  is 
hard.  The  outside  mould  is  placed  on  a  board  or  working  table 
bottom  down.  All  surfaces  that  are  to  come  into  contact  with  the 
concrete  are  shellacked  and  oiled  well.  A  layer  of  concrete  is  then 
poured  into  the  mould,  as  thick  as  the  bottom  of  the  ornament;  the 
core  having  been  shellacked  and  oiled  is  then  set  in  place  on  this  bed 
of  concrete.  The  remaining  concrete  is  poured  around  the  core 
and  well  tamped  and  the  top  is  carefully  smoothed  off.  After  this 
has  set  about  24  hours  the  core  and  outside  mould  are  removed  and 
the  surface  of  the  ornament  is  treated  in  one  of  the  many  ways  sug- 
gested. It"  is  then  laid  aside  to  cure.  It  should  be  wetted  once  or 
twice  a  day  for  a  week  or  two  to  prevent  crumbling. 

In  making  wooden  moulds,  the  core  must  be  made  collapsible 
so  as  to  be  easily  removed,  and  as  few  nails  as  possible  must  be  used 
to  avoid  unnecessary  hammering.  Rounded  or  bevelled  edges  can 
be  obtained  in  wooden  forms  by  using  picture  moulding  and  tri- 
angular strips,  blocks  of  wood,  diamond  shape,  square  or  round  can 
be  tacked  in  the  form,  and  thus  produce  corresponding  indentations 
in  the  concrete.  These  indentations  can  be  filled  with  colored 
cement,  clay  or  tiles,  producing  very  interesting  effects.  Tiles  can 
be  placed  in  the  forms  held  by  light  strings  in  proper  positions  and 
the  concrete  carefully  tamped  around  them.  After  the  concrete 
has  set,  the  string  is  cut,  and  the  form  is  removed,  thus  leaving  the 
tile  in  the  finished  ornament. 

Metal  Moulds. — Forms  made  of  galvanized  sheet  iron  stamped 
and  bent  to  the  desired  lines  have  been  used  with  some  success  as 
moulds  for  concrete  work.  They  can  usually  be  made  by  any  cornice 
mason  and  with  the  bending  machines  used  in  cornice  work.  For 
large  designs  the  sheet  iron  must  be  braced  with  wood  to  prevent 
bending. 


Handbook  for  Cement  and  Concrete  Users 


FlG.  37. — Moulds  for  Orna- 
mented Column. 


Plaster  Moulds. — In  making  concrete  mould  work  with  any  but 
wooden  forms,  the  first  thing  is  to  obtain  a  model.  These  models 
may  be  made  of  wood  for  simple  designs  or  modelled  in  clay,  or 
plaster  of  Paris  for  more  complicated  designs.  Metal  or  China 
ornaments,  vases,  and  jardinieres  can  also  be  reproduced. 

Take  a  simple  case  of  making  a  concrete  box.  First,  construct 
a  box  of  wood  of  the  required  size,  make  the  inside  of  the  box  taper 

slightly  so  that  the  material  is  thicker 
at  the  bottom  than  at  the  top;  this 
will  allow  the  model  to  be  slipped  out 
from  the  mould  when  the  same  is  hard. 
Now  lay  your  wooden  box  upon  a 
working  board,  shellac  and  oil  all  sur- 
faces, and  mix  up  enough  plaster  of 
Paris  to  make  a  layer  about  one-half 
inch  thick  around  the  sides  of  the  box. 
By  means  of  thumb  tacks  or  small 
tacks  attach  a  strip  of  paper  at  each  of 
two  opposite  edges  of  the  box.  This 
paper  is  to  separate  the  mould  and 

make  two  halves  of  it.  Now  apply  the  plaster  to  the  model,  making 
a  wall  about  one-half  inch  thick.  When  this  is  hard,  remove  same 
from  the  box  and  proceed  to  make  the  core  or  inside  portion  of  mould. 
First  shellac  and  oil  well  the  inside  of  the  box,  then  mix  up  sufficient 
plaster  of  Paris  and  fill  the  box  with  same.  Level  off  the  top  and 
allow  to  harden  about  15  minutes,  then  hold  the  box  upside  down 
over  the  working  board  and  tap  gently.  Owing  to  the  taper  of  the 
box,  the  plaster  will  slip  out  easily.  This  core  should  be  smoothed 
off  and  corners  rounded  if  desired. 

All  that  is  necessary  now  is  to  shellac  and  oil  the  parts  of  the 
mould  which  come  in  contact  with  the  concrete  as  well  as  the  working 
board  on  which  they  rest;  properly  centre  the  core  and  outside  walls 
on  the  board,  the  two  parts  of  the  outside  mould  being  held  together 
by  a  string  tied  around  them.  As  they  are  on  the  board  now,  the 
bottom  of  the  box  is  up,  so  that  the  core  must  be  placed  with  its 
largest  side  down.  The  outsides  will  project  up  above  the  core  an 
amount  equal  to  the  thickness  of  the  bottom.  Now  mix  up  your 
concrete  and  pour  same  into  the  annular  layer  between  the  core  and 

[J44] 


The  Making  of  Ornamental   Concrete 

the  outer  mould  and  over  the  core  to  the  top  of  the  mould.  Carefully 
tamp  your  concrete  down  into  he  mould,  preventing  air  holes,  etc. 
When  mould  is  full,  scrape  off  the  top  with  a  straight  edge  and  allow 
to  stand  until  concrete  has  set.  This  takes  about  8  hours.  At 
the  end  of  this  time,  the  mould  can  be  removed  as  follows: 

Gently  tap  the  working  board  on  its  edges  and  it  will  fall  free 
from  the  mould,  then  place  the  mould  and  model  together  on  some 


BOI 


FIG.  38. — Plaster  Moulds  for  Concrete  Baluster.     Sketch  showing  progressive  steps  in 

moulding   same. 

blocks  of  wood  a  few  inches  high  on  the  board,  supported  so  that 
the  concrete  ornament  and  the  outside  mould  rest  on  the  blocks 
and  the  inside  core  is  free.  Gently  tap  the  mould  until  the  core 
drops  out.  The  outside  form  is  next  removed  by  similar  tapping, 
the  string  that  binds  the  two  parts  being  severed. 

To  make  more  complicated  designs  in  plaster  moulds,  all  that  is 

10 


Handbook  for  Cement  and  Concrete  Users 

necessary  is  to  procure  a  model,  and  cover  same  with  plaster,  making 
it  in  so  many  parts  as  to  avoid  all  reentrant  angles,  undercuts,  or 
overhanging  corners.  If  a  core  is  used,  it  can  be  cut  up  into  small 
wedges  so  as  to  be  easily  removed.  Plaster  of  Paris  can  be  cut 
with  a  fine  saw  very  nicely  if  kept  wet. 

Handles  or  ears  to  vases  can  be  moulded  separately  and  fitted 
to  holes  prepared  in  the  vase  and  cemented  in  place. 

Glue  Moulds. — For  designs  in  concrete  which  have  considerable 
undercut,  glue  moulds  have  been  used  almost  exclusively  in  the  past, 
because  they  are  flexible  and  can  be  strained  so  as  to  allow  the 
finished  product  to  be  removed. 

A  glue  mould  can  be  reused  about  six  times  and  the  glue  can  then 
be  boiled  down  and  used  again  for  other  moulds,  but  they  are  not 
quite  so  good  as  plaster  moulds,  which  will  last  indefinitely  if 
handled  carefully. 

Sand  moulds  are  displacing  to  some  extent,  the  use  of  glue 
moulds,  because  of  certain  advantages,  of  which  more  will  be  said 
later. 

In  concrete  work  formed  from  glue  moulds,  as  with  all  other 
mould  work,  a  model  of  the  piece  to  be  formed  must  first  be  ob- 
tained or  made.  The  model  is  laid  on  the  table  or  working  board 
and  a  pencil  line  is  drawn  around  it  on  the  board,  so  as  to  mark  its 
position.  This  enables  the  workman  to  put  the  model  back  again 
in  the  precise  position  after  it  has  been  moved.  The  model  is  next 
covered  with  a  damp  newspaper,  the  paper  being  pressed  into  all  the 
corners  and  angles  of  the  model.  A  layer  of  damp  clay  about  3/4 
of  an  inch  thick  is  then  laid  over  the  model  following  its  contours 
roughly.  Next,  a  plaster  case  is  moulded  over  the  clay,  filling  this 
case  about  3/4  inch  thick,  and  is  made  flat  on  its  outside  so  as  to  be 
able  to  rest  on  this  side  when  in  use.  The  outside  of  the  case  is 
marked  on  the  board  in  the  same  way  as  the  model  was.  When 
the  plaster  case  is  sufficiently  hard,  it  is  removed  and  the  clay  and 
paper  taken  from  the  model  which  is  now  shellacked,  oiled,  and  re- 
placed, in  its  original  position,  by  means  of  the  line  on  the  board. 

The  plaster  case  has  two  holes  bored  into  it,  one  about  3/4  inch 
in  diameter  to  permit  the  glue  to  flow  through  it;  the  other,  a  small 
hole,  to  allow  the  air  to  pass  out  as  the  glue  is  poured  in,  is  bored 
in  the  highest  point  in  the  case,  thus  serving  to  tell  when  the  space 

[146] 


The  Making  of  Ornamental  Concrete 

between  the  model  and  case  is  full,  by  the  glue  coming  out  of  it. 
The  plaster  case  is  next  put  into  the  position  indicated  by  the  line 
on  the  board,  and  fastened  in  this  position  by  straps  passing  over  it. 

The  glue  should  be  of  a  good  quality  of  white  glue;  it  is  heated 
in  a  double  boiler  until  it  is  thin  enough  to  pour.  The  space  be- 
tween the  plaster  case  and  the  model  is  filled  with  the  glue  by  slowly 
pouring  it  into  the  hole  provided  until  it  runs  out  of  the  air  vent.  It 
is  then  allowed  to  stand  about  12  hours  to  congeal.  The  plaster 
case  is  removed,  and  the  glue  mould  is  taken  from  the  model  by 
springing  its  ends  and  sides  slightly  so  as  to  allow  the  undercuts  to 
slip  out  without  injuring  the  model  or  the  mould.  The  mould  is 
kept  in  the  plaster  case  so  as  to  preserve  its  shape. 

Before  using  the  glue  mould,  its  surface  must  be  treated  so  as  to 
make  it  waterproof;  this  is  accomplished  by  washing  it  with  a 
saturated  solution  of  alum.  Two  or  three  coats  are  necessary,  and 
each  coat  must  be  dry  before  the  next  is  applied.  In  lieu  of  the 
foregoing,  the  surface  can  be  varnished  and  oiled. 

Sand  Moulds. — Sand  moulds  are  probably  the  cheapest  moulds  in 
which  concrete  can  be  cast,  and  at  the  same  time  they  offer  some 
advantages  over  all  other  methods  of  moulding.  In  a  sand  mould, 
it  is  of  no  account  how  great  the  undercut  or  how  small  the  orifice 
through  which  the  core  has  to  be  removed,  for  the  sand  after  it  has 
dried  out  can  be  crumpled  into  little  grains  and  poured  out  of  an 
orifice  or  scraped  out  of  an  undercut  with  great  ease  and  without 
possibly  injuring  the  ornament. 

The  process  of  making  artificial  stone  by  casting  in  moistened 
sand  is  described  by  W.  P.  Butler,  the  inventor,  as  follows: 

"Opening  Casting. — The  first  step  in  the  process  is  to  make  a 
wooden  pattern  of  the  stone  to  be  made.  This  pattern  or  model 
is  made  of  the  exact  size  of  the  stone  desired,  and  it  may  be  made 
in  one  or  in  several  pieces.  The  size  and  style  of  the  block  usually 
determine  the  method  to  use  in  the  casting  of  it. 

"The  most  common  method  of  casting  is  that  of  casting  on  the 
floor,  or  'open-casting,'  as  it  is  commonly  called.  Nearly  all  large 
stones  as  well  as  small  ones  are  cast  in  this  way.  The  pattern  is 
embedded  solidly  upon  the  compound  (which  for  brevity  we  will 
call  the  sand),  which  is  then  packed  solidly  around  it  and  built  up 
until  it  is  fully  embedded  in  the  same  manner  that  a  pattern  is  set 


Handbook  for  Cement  and  Concrete  Users 

in  the  sand  in  a  foundry.  To  remove  the  pattern  from  the  sand  it 
should  be  lightly  tapped,  so  as  to  loosen  it  without  noticeably  en- 
larging the  mould,  from  which  it  should  then  be  withdrawn  with  the 
greatest  care  so  as  not  to  break  down  the  edges. 

"If,  on  examination,  the  surfaces  of  the  mould  are  not  perfectly 
smooth,  or  if  any  edge  is  broken  down,  or  if  any  detail  is  imperfect 
or  damaged,  it  may  be  'touched  up'  or  repaired  with  the  moulder's 
tools  which  it  is  necessary  to  have. 

"  One  perfect  mould  having  been  made,  as  many  others  as  are 
desired  can  be  made  in  like  manner  from  the  same  pattern.  A 
competent  moulder  can  make  from  five  to  fifty  moulds  in  a  day, 
according  to  the  difficulty  or  size  of  each.  If  the  pattern  has  no 
projecting  parts  which  would  prevent  its  being  withdrawn  from 
the  sand,  it  may  best  be  made  in  one  piece,  but  if  there  are 
projecting  details  or  undercuts  on  the  pattern,  then  it  must  be  made 
in  two  or  more  pieces  so  as  to  make  it  possible  to  withdraw  it  from 
the  sand  without  breaking  down  the  mould  This  necessitates  not 
only  good  workmanship  on  the  part  of  the  pattern-maker,  but  a 
thorough  knowledge  on  his  part  of  the  necessities  of  the  moulding 
process. 

"The  removal  from  the  sand  of  a  pattern  of  two  or  more  pieces  is 
done  in  the  same  manner  as  though  there  was  but  one  piece,  but 
it  requires  more  time  and  care. 

"Compartment  Casting. — If  the  block  to  be  cast  is  for  a  cornice, 
belt-course,  water-table,  or  any  similar  purpose  where  there  is  an 
ornamental  or  moulded  face,  with  the  other  sides  plain,  a  better 
and  more  rapid  method  of  casting  is  to  fasten  two  planks  on  edge, 
and  parallel  with  each  other,  with  partitions,  fashioned  between 
the  planks  at  proper  distances,  forming  a  series  of  compartments 
in  each  of  which  is  to  be  cast  a  stone.  The  length  of  the  pattern 
or  distance  between  the  planks  is  made  to  equal  the  length  of  the 
block. 

"The  pattern  in  this  case  need  be  only  the  face  of  the  block 
which  is  adjusted  within  the  compartment  at  such  a  distance  from 
the  partition  back  of  it  as  to  give  the  proper  width  to  the  block. 
Then  in  the  space  in  front  of  the  pattern,  solidly  tamp  the  sand. 

"  Next  loosen  the  pattern  and  draw  it  away  from  the  sand,  which 
retains  the  design  of  the  face.  This  process  is  repeated  in  the 


The  Making  of  Ornamental  Concrete 

several  compartments,  and  the  moulds  are  then  filled.  By  this 
method  a  minimum  of  time  is  required  and  blocks  are  formed  much 
more  rapidly  than  when  moulded  in  a  bed  of  material  on  the  floor. 

"Casting  in  Open-end  Flasks.— This  method  will  prove  to  be 
the  best  in  many  cases,  especially  where  it  is  desired  to  pack  the 
moulding  compound  vertically  on  the  face  of  the  pattern.  In  this 
process  a  box  or  collapsible  'flask'  is  open  at  the  top  and  bottom. 
Within  the  flask  and  at  the  proper  distance  from  the  bottom  is 
fastened  the  pattern  or  face-plate. 

"Over  and  upon  the  top  of  the  pattern  tamp  the  sand  and  then 
fasten  over  this  the  cover  to  hold  the  sand  in  position  while  the  flask 
is  being  turned  over.  Next  loosen  and  remove  the  pattern,  leav- 
ing the  mould  ready  for  the  cast,  wherein  the  face  of  the  block 
alone  is  in  the  sand.  When  the  cement  is  hardened  the  flask  is 
loosened  and  removed. 

"Casting  in  Closed  Flask. — Many  pieces,  such  as  balusters, 
balls,  or  similar  turned  forms,  or  forms  which  are  symmetrical  on 
all  sides,  must  be  cast  in  closed  boxes  or  flasks. 

"The  pattern  of  the  baluster  is,  in  the  case  shown,  made  in  two 
pieces  which  are  embedded  in  the  lower  and  upper  halves  of  the 
flask.  The  patterns  are  then  withdrawn  and  the  two  halves  of  the 
flask  are  carefully  locked  together.  The  cast  is  then  made  by 
pouring  the  liquid  cement  through  the  opening  in  the  end  of  the 
flask.  A  great  variety  of  the  finest  ornamental  work  is  cast  in  this 
manner. 

"In  all  cases  the  cement  and  powdered  stone,  in  the  proportions 
of  one  of  cement  to  three  of  stone  dust,  are  mixed  with  water  until 
of  the  consistency  of  thick  gravy,  and  then  carefully  poured  into  the 
mould,  using  a  pouring  board  or  pipe  to  guide  the  stream  and 
prevent  its  tearing  up  the  sand.  The  mass  is  then  allowed  to  set 
and  harden  for  about  a  week  before  it  is  removed  from  the  mould. 
This  protection  of  the  cement  in  the  moistened  mould  prevents  the 
cracking  or  checking  of  the  surface.  When  the  stone  is  fully  dried 
out,  the  surface  is  brushed  off  with  a  wire  brush  to  remove  the 
surplus  sand,  and,  if  a  tooled  appearance  is  desired,  the"  surface  can 
be  gone  over  with  tools  and  then  the  block  cannot  be  distinguished 
from  one  carved  from  the  natural  stone." 


149 


CHAPTER  XV 

CONCRETE  PIPES,  FENCE  POSTS,  ETC.* 

Advantages  of  Concrete  Pipes. — Moulds,  Machines,  and  Manufacture  of  Reinforced 
Concrete  Pipes. — Concrete  Tile,  Data,  and  Costs. — Advantages  of  Concrete  Fence 
Posts. — Moulds,  Machines,  and  Manufacture. — Reinforcement  for  Fence  Posts. 
— Fastening  Fence  to  Posts. — Quantity  of  Materials  for  Fence  Posts. 

CONCRETE  PIPES* 

A  LARGE  amount  of  concrete  pipe  is  now  being  manufactured 
and  used  in  this  country.  They  possess  many  advantages  over 
and  are  far  superior  to  any  other  kind  of  pipe  for  many  purposes. 

Advantages  of  Concrete  Pipe. — Concrete  pipe  can  be  manu- 
factured practically  anywhere.  But  little  equipment  is  required  and 
this  can  readily  be  obtained.  Of  the  material  necessary  for  man- 
ufacture, the  sand  and  stone  can  always  be  found  locally.  The 
cement  may  have  to  be  shipped  some  distance,  but  the  cement 
constitutes  but  a  small  portion  of  the  bulk.  Thus,  easily  obtained 
materials,  low  freight  charges,  and  low  cost  of  equipment  all  make 
for  a  low-priced  pipe.  It  costs  less  to  make  concrete  pipe  than  to 
make  clay  pipe,  and  a  better,  truer,  and  stronger  pipe  is  the  result. 

Properly  made  concrete  pipe  does  not,  under  usual  conditions, 
deteriorate  with  age,  but  instead  grows  stronger.  The  life  of  the 
pipe  is  therefore  indefinite.  This  can  be  said  of  no  other  form  of 
pipe.  If  made  impervious  it  is  immune  from  injury  by  acids,  oils, 
alkali,  and  other  disintegrating  influences  as  explained  in  a  previous 
chapter. 

Concrete  pipe,  if  properly  made,  is  perfectly  shaped  and  is  true 
at  both  ends.  This  uniformity  greatly  simplifies  the  laying  of  the 
pipe,  as  because  of  it  all  members  will  fit  together  easily  and 
accurately. 

*  The  best  treatise  on  cement  pipe  will  be  found  in  "Cement  Pipe  and  Tile,"  by 
E.  S.  Hanson,  editor  of  Cement  Era,  published  by  Cement  Era  Publishing  Co.,  Chicago, 
111. 


Concrete  Pipes,  Fence  Posts,  Etc. 

Enlarged  bells  are  not  necessary  for  the  proper  jointing  of 
concrete  pipes.  The  pipe  therefore  may  be  of  uniform  diameter 
throughout,  which  greatly  facilitates  bedding  and  aligning. 

Concrete  pipe  is  not  limited  to  the  circle  in  shape,  but  may  be 
varied  to  suit  the  conditions.  Where  the  flow  is  variable  the  egg 
shape  may  be  desired,  and  again  where  a  greater  area  of  bed  is 
necessary  a  pipe  with  a  flattened  invert  may  be  decided  upon. 
Such  shaped  pipes  may  be  as  readily  made  in  concrete  as  the  more 
generally  used  circular  ones. 

Concrete  pipe  maybe  made  of  any  strength  desired  by  intro- 
ducing suitable  reinforcement.  It  may,  therefore,  be  used  for  pipes 
under  pressure. 

Manufactured  vs.  Cast-in-Place  Pipe. — When  compared  with  a 
concrete  pipe  cast  in  place,  the  following  advantages  are  claimed  for 
a  concrete  pipe,  made  in  short  lengths  in  some  convenient  place,  and 
then  laid. 

The  pipe  may  be  readily  inspected  both  during  and  after  manu- 
facture. 

Reinforcing  metal  may  be  accurately  placed  and  kept  in  place 
until  the  concrete  has  been  poured. 

The  forms  may  be  used  over  and  over  again,  thereby  decreasing 
the  cost  of  the  pipe. 

Being  laid  in  short  lengths,  each  length  may  be  allowed  to 
settle  firmly  on  its  bed  before  closing  the  joints.  In  large  pipes  the 
back  fill  may  even  be  placed  before  cementing  the  joints.  This 
minimizes  the  danger  of  the  pipe  straining  or  cracking  due  to  unequal 
settlement.  Also,  under  these  conditions,  when  once  closed  there 
should  be  little  or  no  tendency  for  the  joints  to  reopen. 

The  disadvantage  of  a  pipe  laid  in  short  sections  is  the  number 
of  joints.  These  joints  are  of  necessity  the  weakest  part  of  the  pipe, 
and  are  therefore  the  controlling  element.  This  inherent  weakness 
is  overcome  to  a  certain  extent  by  various  special  methods,  as  the 
use  of  metal  ties  between  sections,  or  by  lapping  the  reinforcement 
of  one  section  over  that  of  the  next. 

Moulds,  Machines,  and  Manufacture. — Various  kinds  of  moulds 
and  machines  for  the  manufacture  of  concrete  pipe  have  been  de- 
signed and  patented. 

The  simplest  of  these  consists  of  an  iron  pallet,  an  outer  hinged 


Handbook  for  Cement  and  Concrete  Users 

shell  and  an  inner  collapsible  core,  both  of  sheet  steel,  a  cap  to  fit 
over  the  core  and  a  tamper.  To  these  may  be  added  an  attachment 
for  forming  a  bell  end  on  the  pipe.  The  method  of  using  is  as 
follows : 

The  iron  pallet  is  placed  on  the  floor,  the  core  is  backed  inside 
and  the  conical  cap  is  placed  over  it.  The  outer  shell  is  then  backed 
in  place,  and  the  mould  is  ready  to  be  filled.  Concrete  is  shovelled 
in  a  little  at  a  time  and  thoroughly  tamped.  The  whole  outfit  is 
then  removed  to  the  curing  shed  where  the  inner  core  is  first  collapsed 
and  removed,  then  the  outer  shell  expanded  and  removed,  leaving 
the  finished  pipe  standing  on  the  pallet. 

The  "Schenk  Siam"  tile*  machine  consists  essentially  of  a 
pyramidal  frame  about  8'  high,  a  revolving  table  for  carrying  moulds, 
a  revolving  shaft  carrying  the  packer  head,  a  loot  from  which  the 
moulds  are  filled,  and  a  bucket  elevator  which  delivers  .the  concrete 
to  the  loot. 

The  tile  are  made  in  galvanized  iron  jackets,  made  in  two  parts, 
and  provided  with  hinges  and  lock.  These  jackets  are  set  on  pallets 
carried  by  the  revolving  table,  the  table  carrying  six  pallets  of  any 
size.  These  pallets  are  held  by  pins  in  the  table,  the  change  from  one 
size  to  another  being  made  by  simply  lifting  off  one  set  of  pallets 
and  dropping  another  into  place. 

The  table  is  revolved  and  the  jacket  placed  in  a  position  for 
making  tile  by  means  of  a  cam  at  the  rear  of  the  machine.  There 
is  a  ring,  or  rather  a  combination  ring  and  a  small  hopper, 
which  drops  down  on  to  the  jacket  after  it  is  revolved  into  posi- 
tion, and  holds  the  jacket  solidly  in  position  while  the  tile  is 
being  made. 

When  the  jacket  is  in  place,  the  packer  head,  which  is  on  a 
sliding  shaft,  operated  by  another  cam  at  the  rear  of  the  machine, 
drops  down  through  the  jacket  and  into  and  fills  the  bottom  ring; 
and  just  at  this  point,  where  the  packer  fills  the  ring,  the  concrete 
is  dumped  in  from  the  top  by  means  of  the  elevator.  The  cup  on 
the  elevator  holds  just  enough  material  to  make  a  tile,  different  cups 
being  put  on  for  the  different  sizes.  Thus  the  concrete  is  dumped 
down  inside  of  the  jacket  and  around  the  packer,  and  the  packer 

*  From  "  Cement  Pipe  and  Tile,"  by  Hanson. 


Concrete  Pipes,  Fence  Posts,  Etc. 

head  revolves  up  through  the  concrete  and  packs,  forces,  and  presses 
the  material  between  the  jacket  and  the  packer.  This  packer  head 
has  concave  sides  and  is  graduated  out  from  the  size  of  shaft  on 
which  it  revolves,  to  the  full  size  of  the  inside  of  the  tile  at  the  lower 
end.  Thus,  it  is  in  one  sense  the  core,  for  it  forms  the  inside  of  the 
tile,  and  revolves  up  out  of  the  jacket  through  the  top  ring,  and  the 
ring  rises  with  it  and  releases  the  jacket,  and  the  tile  is  made;  then 
the  table  revolves  and  another  jacket  moves  into  place. 

As  the  tile  are  made  they  are  removed  from  the  machine  and  taken 
to  the  drying  shelves  where  the  jackets  are  taken  off. 

The  machine  has  a  square  upright  plane  and  the  pallets  are 
carried  on  a  sliding  rack  which  holds  two  pallets,  so  that  as  one 
finished  tile  is  carried  away,  another  jacket  slides  into  place.  The 
power  head  is  made  in  two  parts,  the  main  part  attached  to  the 
shaft  revolving  at  one  speed  while  the  wings  attached  to  the  outer 
shaft  revolve  at  a  much  higher  speed,  pressing  the  concrete  outward 
against  the  walls  of  the  jacket  and  trowelling  it  down  smooth. 

When  the  carriage  is  at  its  highest  point  the  head  fills  the  lower 
ring,  or  pallet;  then  the  concrete  is  dumped  in  automatically;  the 
head  revolves  continually  and  forms  the  tile.  When  the  carriage 
is  at  its  lowest  point  the  table  shifts  automatically  and  the  tile  in  the 
jacket  is  taken  to  the  curing  shelves,  where  the  jacket  is  removed 
immediately  and  returned  to  the  machine. 

The  machine  is  set  in  motion  by  a  lever  which  operates  a  friction 
clutch.  The  lever  at  the  left  of  the  machine  is  used  to  start  the 
cable.  After  this  is  put  in  motion,  the  concrete  is  thrown  into  the 
hopper,  the  buckets  taking  up  a  sufficient  amount  for  one  tile. 
This  is  dumped  in  just  at  the  time  the  carriage  is  at  its  highest  point. 
The  head  at  once  presses  the  concrete  against  the  jacket  and  as  the 
carriage  is  lowered,  the  tile  is  formed.  The  cable  then  shifts  to  one 
side,  putting  the  finished  tile  in  position  to  be  put  away  and  bringing 
another  jacket  into  position  under  the  tamper.  The  machine  makes 
tile  from  4  to  16  inches  in  diameter. 

The  Miracle  Power  Tile  Machine  consists  of  a  base  from  which 
rises  a  hollow  shaft  carrying  the  operating  mechanism,  and  around 
which  shaft  revolves  the  table  carrying  the  moulds. 

The  tile  are  made  by  means  of  a  peculiarly  shaped  revolving 
packer  which  operates  inside  the  steel  mould  or  casing.  The  circular 


Handbook  for  Cement  and  Concrete  Users 

table  around  the  column  of  this  machine  is  moved  vertically  by  the 
mechanism  and  carries  the  casing  with  it.  When  the  table  or 
carriage  is  at  its  highest  point  the  packer  completely  fills  the  ring  or 
pallet  upon  which  the  casing  rests.  At  this  moment  the  machine 
automatically  dumps  the  proper  amount  of  concrete  into  the  casing, 
which  then  goes  downward  with  the  table  and  the  revolving  packer 
gradually  moves  up  inside  the  casing,  forcing  and  packing  the  con- 
crete against  the  latter  and  forming  the  tile.  When  the  casing  reaches 
the  bottom,  the  packer  and  casing  are  free  and  the  table  revolves 
and  brings  the  next  casing  into  position,  and  the  operation  is  re- 
peated. In  the  meantime  the  tile  are  carried  away  in  the  casing  to 
the  curing  shelves.  The  casing  is  then  removed  from  the  tile  and 
returned  to  the  machine  to  be  used  over  again. 

The  packer  head  of  this  machine  is  made  reversible,  so  that 
when  worn  out  in  one  position  by  the  grinding  action  of  the  sand, 
it  can  be  used  in  another. 

The  manufacturers  claim  that  6  to  8  horse-power  is  ample  for 
operating  the  machine. 

In  the  manufacture  of  concrete  pipe,  the  concrete  used  is  of  a 
sufficient  consistency  to  permit  of  the  immediate  removal  of  the 
moulds.  The  mixture  is  therefore  comparatively  dry. 

After  the  pipe  is  moulded  it  is  taken  to  the  curing  shed  where  it 
remains  from  four  to  seven  days,  during  which  time  it  is  kept  con- 
stantly moist  by  frequent  sprinkling.  In  some  plants  steam,  under 
low  pressure,  is  used  in  the  curing  shed.  This  assures  an  equal 
distribution  of  moisture,  and  under  this  condition  it  is  impossible 
for  any  pipe  to  dry  out. 

After  curing,  the  pipes  are  taken  to  the  drying  yard.  Here 
they  may  or  may  not  be  sprinkled  occasionally,  depending  upon 
atmospheric  conditions.  Pipe  is  kept  in  the  drying  yard  until  it 
is  about  30  days  old,  when  it  is  ready  for  laying. 

Reinforced  Concrete  Pipe. — Various  forms  of  reinforced  concrete 
pipe  have  beert  used  where  the  strength  of  the  manufactured  pipe 
is  insufficient.  They  are  reinforced  either  by  steel  rods  in  flats 
placed  both  circumferentially  and  longitudinally  or  by  wire  mesh 
or  expanded  metal.  Particular  attention  is  now  being  paid  to  the 
joints,  the  object  being  to  make  the  joint  equally  as  strong  as  the 
rest  of  the  pipe,  thus  giving  a  truly  monolithic  pipe  line. 


Concrete  Pipes,  Fence  Posts,  Etc. 

The  Jackson  Concrete  Pipe  is  one  where  particular  attention 
has  been  given  to  the  method  of  jointing. 

This  pipe  is  manufactured  in  sizes  ranging  from  24  to  108  inches. 
The  forms  for  making  this  pipe  are  assembled  by  first  setting  up 
the  inner  wall  in  rolled  sheet  sections  on  the  upper  and  inner  flange 
of  the  bottom  plate  or  ring.  The  lateral  reinforcement,  consisting  of 
steel  slabs,  is  inserted  in  pockets  in  this  ring.  The  circumferential 
reinforcing,  consisting  usually  of  one  or  two  cylinders  of  triangular 
mesh  reinforcement  is  now  placed,  after  which  the  outer  wall  is 
assembled  on  the  lower  or  outer  flange  of  the  bottom  plate.  Space 
clips  at  the  top  of  the  wall  hold  the  reinforcement  in  position. 
The  mould  is  then  filled  and  rammed  by  hand. 

The  longitudinal  reinforcement  extends  beyond  the  sections 
and  terminates  in  hooked  ends  which  fit  into  the  rebated  space 
which  forms  an  outside  groove,  when  the  two  sections  are  placed 
together.  The  sections  are  then  interlocked  with  a  tie  band  pass- 
ing completely  around  the  pipe  at  the  groove  and  through  the 
hooked  ends  of  the  longitudinal  reinforcing  bars.  A  joint  shield 
is  then  drawn  up  snugly  around  the  pipe  and  the  joint  first  flushed 
with  water  and  then  grouted. 

In  the  latest  form  of  this  pipe,  the  pipe  is  so  shaped  that  the 
lower  half  of  the  groove  is  on  the  inside  and  the  upper  half  is  on 
the  outside  of  the  pipe.  In  this  case  the  lower  half  of  the  joint  is 
interlocked  and  grouted  from  the  inside  and  the  upper  half  from 
the  outside. 

This  pipe  is  usually  manufactured  at  the  trench.  Local  labor 
and  material  are  therefore  used  and  there  are  little  or  no  freight 
charges.  This  method  also  leaves  the  pipe  open  for  inspection  at 
all  times. 

Another  pipe,  where  the  distinctive  feature  is  the  method  of 
jointing,  is  the  Lock  Bar  Pipe  (Meriwether  System). 

This  pipe  is  manufactured  in  sizes  ranging  from  24  to  96  inches 
in  diameter  and  in  either  three-  or  four-foot  lengths.  The  standard 
pipe  has  a  circular  section.  The  reinforcement  is  placed  concentric 
with  the  circumference  of  the  pipe  and  toward  the  interior  of  the 
section.  Each  section  is  cast  with  a  bell  and  a  spigot  end.  The 
bell,  however,  does  not  project  beyond  the  circumference  of  the  pipe, 
but  is  flush  with  it. 


Handbook  for  Cement  and  Concrete  Users 

For  unusual  conditions,  a  pipe  of  special  design  with  a  flat  base 
section  is  made.  In  pipes  of  this  design,  the  reinforcement  is 
placed  toward  the  interior  of  the  crown  and  inverted  toward  the 
exterior  at  the  sides. 

Usually  in  the  expanded  metal  or  American  Steel  &  Wire  Co.'s 
Triangular  Mesh,  the  reinforcing  metal  extends  throughout  the 
length  of  the  section  and  projects  both  into  the  bell  end  and  out  of 
the  spigot  end  for  several  inches.  The  spigot  is  shorter  than  the 
bell,  so  that  when  two  sections  of  the  pipe  are  placed  together  the 
reinforcing  metal  from  one  section  overlaps  the  reinforcement  of 
the  other  section  in  an  internal  recess.  The  recess  in  this  joint  is 
filled  with  cement  mortar,  thus  locking  the  section  together  and 
sealing  the  joint  at  one  operation.  On  all  pipe  of  36  inches  in 
diameter,  or  larger,  the  joints  are  made  from  the  interior  after  the 
back  filling  has  been  placed  by  forcing  grout  behind  a  shield*  with 
a  grout  gun.  On  sizes  less  than  36  inches  in  diameter  the  joints 
are  made  from  the  outside  through  openings  in  the  crown  portion 
of  the  bells  before  the  back  filling  is  placed.  By  placing  the  back 
filling  before  the  joints  of  the  larger  pipe  are  sealed,  any  settle- 
ment caused  by  the  fill  will  occur  before  the  joint  is  made;  thus 
any  strain  on  the  joints  that  would  tend  to  injure  their  efficiency  is 
eliminated. 


TABLE  XIII.— CONCRETE  TILE  DATA  AND  COSTS.* 


Inside  Diameter 
of  Tile  in  Inches. 

Thickness  of  Walls 
in  Inches. 

No.  of  Tile  from 
Bag  of  Cement. 

Cost  per  Tile  for 
Cement  at  $1.50 
per  Bbl.  2-Foot 
Lengths. 

No.  of  Tile  from 
Yard  of  Sand. 

i 

^£ 

|i 

fei  - 
fsi*l 

FstP 

Cost  per  Length 
for  Labor  $2.50 
and  $1.75. 

Total  Cost  per 
Length. 

Total  Cost  per 
Foot  of  Cement 
Tile. 

Average  Selling 
Price  Clay  Tile, 
per  Foot. 

6 

,1 

10 

$0.03 

60 

$0.02 

00 

$o  06 

$0.11 

$0.06 

$0.15 

8 

ii 

6i 

.06 

45 

.  02 

07 

•  J5 

.08 

.  20 

10 

if 

5 

.09 

32 

.03 

7o 

08 

.  20 

.  10 

•  30 

I  2 

i£ 

3 

.  12 

25 

.04 

65 

09 

•  25 

•  13 

.36 

\l 

i^ 

2 

i  9/10 

.18 
.  2  I 

19 
16 

•05 
.06 

57 
50 

10 

ii 

•  33 
•  38 

ill 

2O 

2 

rj 

•24 

14 

.07 

45 

12 

•  43 

.  22 

I  .00 

24 

2? 

I    I/IO 

•  34 

9 

.  ii 

40 

.14 

•59 

•30 

1  .50 

30 

2* 

^ 

•45 

7 

.14 

35 

.16 

•75 

•38 

2.00 

36 

3 

§ 

.60 

6 

30 

.18 

•  96 

.48 

2-50 

42 

-?  r 

-£. 

•  75 

r 

20 

1  7 

35 

i  .30 

.65 

48 

4 

1 

i  •  15 

3i 

•30 

10 

•65 

2.  10 

i  -05 



*  Besser  Manufacturing  Co. 


Concrete  Pipes,  Fence  Posts,  Etc. 


CONCRETE  FENCE  POSTS 

Principal  Advantages. — Owing  to  the  decreasing  supply  of 
available  timber,  the  cost  of  wooden  fence  posts  is  constantly  in- 
creasing. This,  together  with  their  short  life,  makes  imperative 
the  adoption  of  some  other  form  of  fence  post. 

The  ideal  fence  post  should  be  cheap,  strong,  and  permanent. 


FIG.  39. — Artistic  Corner  Fence  Post  Construction. 

f 

These  three  qualifications  are  possessed  only  by  reinforced  concrete 
posts. 

Wood  posts,  as  before  stated,  are  becoming  expensive,  and 
owing  to  their  being  subject  to  decay,  and  damage  by  fire,  their 
life  is  at  best  short. 

Steel  posts  have  been  tried,  but  are  expensive,  and  unless  con- 
stantly painted  will  soon  deteriorate  by  rusting. 

Reinforced  concrete  posts,  however,  are  cheaply  and  easily 
made,  may  be  as  strong  as  desired,  and  are  practically  everlasting. 
Reinforced  concrete  posts  may  be  made  near  their  final  location, 
of  material  obtained  locally,  necessitating  very  little  cartage  and  the 
importation  of  only  a  comparatively  small  amount  of  cement  and 
reinforcing  steel. 

The  manufacture  of  a  reinforced  concrete  fence  post  is  a  com- 
paratively simple  operation.  A  suitable  mould  is  made  or 
procured  and  the  reinforcement  placed  in  it.  The  mould  is 
then  filled  with  concrete,  which  is  then  compacted.  If  a  dry 
concrete  has  been  used,  the  moulds  may  be  removed  imme- 
diately; if  the  concrete  was  wet,  the  post  should  remain  in  the 
moulds  about  24  hours.  After  being  removed  from  the  moulds 

[i57] 


Handbook  for  Cement  and  Concrete  Users 

the  post  should  be  cured  and  dried  in  the  same   manner  as  de- 
scribed for  concrete  pipes. 

Moulds,  Machines,  and  Manufacture. — Various  moulds  and  ma- 
chines for  the  manufacture  of  concrete  fence  posts  have  been  made 


FIG.  40. — Concrete  Fence  Posts  and  Accessories. 

and  are  on  the  market,  all  of  which  appear  to  be  more  or  less 
satisfactory. 

Simple  moulds,  such  as  could  be  made  by  almost  any  man, 
consist  of  two  end  pieces  having  notches  which  hold  in  place  the 
longitudinal  boards.  Cross-pieces  or  hooks  are  provided  to  prevent 

PLANT   FOR   150   POSTS   A   DAY 


FIG.  41. — Layout  of  Plant  for  Making  Concrete  Fence  Posts. 

the  longitudinal  pieces  from  bulging.  The  mould  is  placed  on  a 
platform,  oiled  or  soaped,  after  which  the  post  may  be  made  as 
described  above. 

The  "Haas"  Post  Machine  is  8'  8"  long,  and  28"  wide,  weighs 
about  300  Ibs.,  and  is  made  of  2"  high-grade  cypress  lumber  rein- 
forced with  steel  trussed  bands  and  bolts.  The  machine  is  treated 
to  two  coats  of  oil  and  white  lead. 


Concrete  Pipes,  Fence  Posts,  Etc. 

The'"D.  &  A."  Post  Moulds  are  made  from  one  piece  of  sheet 
steel  about  1/16"  thick.  They  are  U-shaped  in  sections  with 
flanges  bent  at  right  angles  to  the  body  of  the  moulds  to  stiffen  them. 
The  moulds  .are  provided  with  square  detachable  sheet  steel  end 
plates,  which  fasten  to  the  moulds  by  means  of  projections  which 
fit  into  slots  in  the  flange  of  the  mould  and  a  clasp  riveted  to  the 
bottom  of  the  moulds  at  the  ends.  These  end  plates  serve  to  hold 
the  moulds  upright  as  well  as  to  hold  the  sides  of  the  mould  together. 
The  post  is  released  by  removing  the  square  end  pieces.  These 


FIG.  42. — A  Set  of  Six  Post  Machines,  Showing  Method  of  Piling  One  Machine  on  the 
Other.  Can  be  run  under  the  Mixer  and  through  the  Kilns  or  direct  to  curing  rails. 

moulds  are  usually  set  up  ten  at  a  time  on  a  shaker,  and  after  rilling, 
the  concrete  is  compacted  by  agitating  the  shaker. 

The  "Ohio"  Post  Machines  consist  of  two  strong  cast-iron  end 
frames  into  which  are  fitted  six  or  twelve  moulds  of  2O-gauge  sheet 
iron.  The  ends  fit  tightly  between  lugs  cast  on  the  frames  so  that 
the  moulds  are  sprung  slightly  to  gether  in  placing,  thus  when  remov- 
ing the  moulds,  the  sides  will  spring  away  from  the  posts.  Two  side 
rails  hold  the  end  moulds  in  position.  One  side  rail  is  removed  when 
placing  or  removing  the  moulds.  To  compact  the  concrete  the 
frames  are  placed  on  a  shaker  and  agitated.  The  finished  post  is 
T-shaped  in  cross-section. 


Handbook  for  Cement  and  Concrete  Users 


The  "Scott"  concrete  fence  post  mould  is  of  galvanized  iron, 
shaped  to  contain  the  post  face  up  in  its  plastic  form.  The  form 
is  placed  in  a  rack  which  holds  four.  After  placing  the  reinforce- 
ment and  concrete,  and  as  soon  as  the  concrete  has  taken  its  initial 
set,  the  face  of  the  post  is  corrugated  by  a  special  tool  for  same. 
To  remove  the  posts  the  racks  are  set  on  end  with  the  small  end  of 
the  post  on  top.  One  man  then  pushes  the  forms  out  of  the  rack 
while  the  other  takes  care  of  the  posts. 

In  the  foregoing  moulds  a  wet  mixture  of  concrete  is  usually 
used.  The  post  must  therefore  be  left  in  the  moulds  for  a  period 
of  about  24  hours,  thereby  necessitating  a  number  of  moulds.  The 


FlG.    43. — Moulds    for    Fence    Posts,    all    Sides    Tapering. 

manufacturers  of  these  machines  claim  that  this  loss  in  frames  is 
more  than  offset  by  the  increased  strength  of  the  post  resulting  from 
the  use  of  the  wet  mixture. 

In  the  following  moulds  a  dry  mixture  of  concrete  is  used,  and 
the  mould  removed  immediately.  In  this  way,  with  but  one  mould, 
innumerable  posts  may  be  made  without  loss  of  time.  Pallets  of 
some  sort  are  necessary  with  these  machines. 

The  " Bulldog"  Cement  Post  Machine  consists  of  an  angle  iron 
frame  to  which  is  riveted  a  corrugated  steel  apron,  thus  forming 
the  sides  of  the  moulds  and  giving  the  post  its  characteristic  corruga- 
tions. Hinged  end  gates  are  fitted  to  these  sides  which  when  inter- 
locked, permit  the  sides  to  be  spread  and  the  post  thus  released. 

The  " Monarch"  Post  Machine  is  made  entirely  of  steel  and 
is  composed  of  a  double  frame  securely  braced  and  bolted  together. 


Concrete  Pipes,  Fence  Posts,  Etc. 


The  inside  walls  are  hung  on  double  hinges  so  that  the  slightest 
upward  motion  of  the  moulds  releases  the  post. 

The  "Bailey"  Post  Machine  is  made  of  cast  metal.  The  sides 
taper  and  are  hinged  at  the  top.  A  hinged  bottom  plate  holds  the 
sides  together.  To  release  the  post,  the  hinged  bottom  plate  is 
removed  and  the  sides  spread. 

The  "Scott"  Concrete  Fence  Post  Machine  is  made  of  steel  and 
makes  a  post  with  a  U-shaped  cross-section.  This  machine  differs 
from  the  other  in  that  it  must  be  turned  over  to  release  the  post. 

The  "Luck"  Cement  Post  Mould  is  made  in  two  sections  of 
heavy  galvanized  iron,  held  together  by  clamps  on  the  flange.  The 


FIG.    44.— The    Scott    Fence    Post    Machine. 

posts  are  octagonal  in  shape  and  are  cast  in  a  vertical  position,  using 
wet  concrete.  It  is  practically  the  only  post  mould  in  which  the 
post  is  cast  in  a  vertical  position. 

Methods  of  Reinforcement. — Various  methods  of  reinforcing 
fence  posts  are  in  use  and  recommended  by  the  various  manu- 
facturers. The  advantages  of  some  of  these  systems  of  reinforce- 
ment are  more  fanciful  than  real,  and  in  some  cases  the  reinforce- 
ment recommended  would  materially  increase  the  cost  of  the  post. 
For  ordinary  conditions,  plain  rods,  wire,  etc.,  may  be  used  and 
entirely  satisfactory  results  obtained.  Scrap  steel  may  frequently 
be  used  to  advantage.  The  matter  of  reinforcement  should  depend 
entirely  on  what  is  most  easily  and  economically  available.  For  posts 
ii  [161] 


Handbook  for  Cement  and  Concrete  Users 


where  a  dry  concrete  is  used,  however,  some  sort  of  mechanical  bond 
between  the  reinforcing  and  the  concrete  would  be  advisable. 

TABLE  XIV. — QUANTITY  OF  MATERIAL  FOR  FENCE  POSTS.* 

All  posts  are  4  X  5  inches  at  top;  all  posts  are  5  X  6  inches  at  bottom.  One-half 
small  single  load  f  of  sand  required  per  barrel  of  cement;'  one  small  single 
load  f  of  screened  gravel  or  stone  required  per  barrel  of  cement.  Propor- 
tion: i  part  "Atlas"  Portland  cement;  2  parts  sand;  4  parts  gravel  or  stone. 


Length  of  Posts, 
Feet. 

No.  of  Posts  per  Barrel 
(4  Bags)  of  Cement. 

Weight  per  Post, 
Pounds. 

5 

20 

130 

6 

17 

1  60 

7 

14 

1  80 

8 

12 

210 

9 

II 

234 

Methods  of  Fastening  Fence  to  Posts. — Various  methods  of 
fastening  the  fence  to  the  post  are  in  use  at  the  pres- 
ent time,  a  few  of  which  follow. 

Removable  pins  in  the  moulds  form  holes 
through  the  concrete  posts,  which  holes  receive 
long  wire  staples  which  clinch  at  the  back  of  the 
post.  These  staples  can  be  replaced  at  any  time. 

Another  method  consists  of  a  tie  wire  passed 
around  the  post  and  then  twisted  tightly  around  the 
longitudinal  fence  wire.  This  method  would  appear 
to  be  particularly  satisfactory  where  the  face  of  the 
post  is  corrugated. 

A  variation  of  the  above  in  which  one  contin- 
uous binding  wire  is  used  instead  of  a  number  of 
short  pieces. 

The  advantage  of  this  and  the  above  method  is 
that  the  position  of  the  ties  does  not  have  to  be 
determined  in  advance,  but  may  be  readily  shifted 
to  suit  any  position  of  the  fence  wires. 

In  another  method,  holes  are  made  in  the  con- 
crete into  which  wires  are  inserted.  These  wires 


FIG.    45.  — 

Method  of  Fas- 
tening Fence  to 
Post. 


*  From  "  Concrete  Construction  Around  the  Home  and  on  the  Farm,"  published 
by  the  Atlas  Portland  Cement  Co. 
f  Small  single  load  =15  cubic  feet. 

[162] 


Concrete  Pipes,  Fence  Posts,  Etc. 

are  then  carried  to  the  front  of  the  post  and  wrapped  tightly  around 
the  fence  wire. 

In  the   "Monarch"  Fasteners   and  Spring   Steel   Staples,  the 
fastener  is  inserted  in  the  post  while  same  is  being  manufactured. 


FIG.  46. — Method  of  Hanging  Gate  on  Fence  Post. 

The  staple  is  inserted  in  the  fastener  by  means  of  a  pair  of  pliers 
made  especially  for  the  purpose. 

The  "  Taut  wire "  Fence  fastener  is  moulded  into  the  post  when 


TABLE  XV. — QUANTITY  OF  MATERIAL  FOR  CORNER  POSTS.* 

One-half  small  single  load  f  of  sand  required  per  barrel  of  cement;  one  small 
single  load  f  of  screened  gravel  or  stone  required  per  barrel  of  cement. 
Proportions:  i  part  "Atlas"  Portland  cement  to  2  parts  sand  to  4  parts  gravel. 


SIZE  OF  POSTS. 

No.  of  Posts  per 
Barrel  (4  Bags) 
Cement. 

Weight  per  Post, 
Pounds. 

Length,  Feet. 

Top,  Inches. 

Bottom,  Inches. 

6 

12 

12 

»l 

900 

7 

12 

12 

22 

1,050 

8 

12 

12 

21 

I,2OO 

9 

12 

12 

2 

i,35° 

9 

10 

10 

3 

940 

9 

6 

6 

8 

337 

7 

24 

24 

1 

4,200 

*  From  "  Concrete  Construction  Around  the  Home  and  on  the  Farm,"  published 
by  the  Atlas  Portland  Cement  Co. 

t  Small  single  load  =15  cubic  feet. 


Handbook  for  Cement  and  Concrete  Users 

same  is  being  manufactured.     To  hold  the  fence  a  common  wire 
staple  is  driven  into  +he  fastener. 

In  all  wire  fences  considerable  tension  must  be  put  on  the  wires 
if  a  satisfactory  fence  is  to  result.  To  resist  this  tension  occasional 
fence  posts  should  be  braced,  and  in  no  case  should  this  bracing  be 
omitted  at  the  corner  posts,  and  the  post  in  many  cases  should  be 
made  heavier  than  the  posts  in  the  rest  of  the  fence. 


SECTION  IV 

PRINCIPLE  OF  DESIGN  AND  CON 

STRUCTION  IN  REINFORCED 

CONCRETE 


CHAPTER  XVI 

ESSENTIAL  FEATURES  AND  ADVANTAGES  OF  REIN- 
FORCED CONCRETE 

REINFORCED  concrete  is  the  term  applied  to  that  combination  of 
concrete  and  steel  wherein  each  element  of  the  combination  lends 
a  helping  hand  to  make  up  for  the  deficiency  in  strength  of  the  other. 
The  proverb  that  "In  Union  There  is  Strength,"  was  never  more 
exemplified  than  in  the  combination  of  two  materials,  different  in 
so  many  respects  yet  acting  together  as  a  unit  in  resisting  any  in- 
fluences that  tend  to  disrupt  the  structure  built  therefrom. 

Beginning  with  the  building  of  flower  pots  by  a  French  gardener 
40  years  ago,  the  business  of  reinforced  concrete  had  a  haphazard 
growth  for  over  twenty  years,  owing  to  unfamiliarity  with  the  nature 
of  the  materials,  distrust  on  the  part  of  consumers  and  antagonism 
of  union  labor.  Through  the  establishment  of  safe,  rational,  and 
scientific  methods  of  design,  made  possible  by  tests  and  studies 
carried  on  consistently  by  men  like  Melan,  Hennebique,  Ransome, 
Considere,  Hyatt,  Thatcher,  Thompson,  and  others,  confidence 
has  given  place  to  distrust  and  what  only  ten  years  ago  was  looked 
upon  with  suspicion  is  now  hailed  as  a  blessing.  The  fire  at  Balti- 
more and  the  earthquake  and  fire  at  San  Francisco  have  removed 
the  last  lingering  doubt,  and  constructors  are  now  agreed  that  in 
point  of  fireproofness,  and  the  ability  to  withstand  severe  shock  and 
strains,  reinforced  concrete  has  no  equal  among  structural  materials. 


Handbook  for  Cement  and  Concrete  Users 

Concrete  itself  is  very  weak  in  resisting  tension,  or  pulling  strains, 
and  possesses  but  little  elasticity,  while  steel,  on  the  other  hand, 
possesses  both  these  qualities  in  a  high  degree.  It  is  thus  that  the 
introduction  of  steel  converts  a  practically  inelastic  body  into  one 
possessing  a  high  degree  of  elasticity,  and  thus  results  in  a  material 
having  the  following  inherent  qualities:  strength,  which  increases 
with  time,  lightness,  rapidity  of  construction,  and  many  other  im- 
portant advantages.  So  much  are  the  resisting  properties  increased 
that  reinforced  concrete  is  bound  to  supplant  almost  entirely  brick 
and  stone  masonry  in  most  all  of  the  forms  of  construction  into 


BEAM 


6'S' 


':'',  $>>  /'• ;  ^f$jjf$fr$, 

'  '•"JQ"*'':^  :    .  1  'V.TV&t5?V 


FIG.  47. — Comparative  Sizes  of  Plain  and  Reinforced  Concrete  Beam  for  Same  Span 

and  Loading. 

which  the  latter  so  largely  enters,  particularly  in  such  structures  as 
factories,  walls,  sewers,  aqueducts,  bridges,  arches,  chimneys,  dams, 
tanks,  foundations,  etc. 

The  economy  of  reinforced  concrete  arises  also  from  the  fact 
that  unskilled  labor  may  be  employed  in  the  work,  and  owing  to  its 
inherent  strength  a  great  saving  in  material  and  space  is  made 
possible  over  ordinary  brick  and  stone  construction.  There  are 
also  some  disadvantages  attending  its  use,  such  as  the  necessity  for 
wooden  forms  and  the  difficulties  which  attend  their  use,  but  these 
are  more  than  offset  by  the  accompanying  benefits. 

Ease  and  rapidity  of  erection  arise  from  the  fact  that  walls 
can  be  quickly  moulded  and  floors  and  roofs  are  moulded  at  the  same 
time  as  the  beams  which  support  them.  No  dressing  or  dimension 
cutting  is  required  and  material  is  readily  procured  in  all  localities. 

The  fireproofness  of  concrete  is  due  to  the  fact  that  i*  is  a  very 
poor  heat  conductor.  It  expands  and  contracts  at  the  same  rate 
as  the  reinforcing  steel  and  there  is  no  tendency  of  separation  be- 

[166] 


Essential  Features  of  Reinforced  Concrete 

tween  them.  In  fact,  the  bond  or  adhesion  of  concrete  to  steel  is 
very  strong  and  is  an  important  element  in  the  design  of  reinforced 
concrete  work,  as  it  is  due  to  this  very  adhesive  property  that  strains 
coming  upon  the  concrete  are  partly  taken  up  by  the  steel,  for  with- 
out such  adhesion  they  could  not  act  as  a  unit. 

The  bond  between  the  concrete  and  steel  is  due  both  to  friction, 
molecular  adhesion,  and  shrinkage  of  the  concrete  during  the 
process  of  setting  or  hardening  which  causes  it  to  take  a  hard,  firm 
grip  on  the  steel.  The  proportion  of  the  strain  taken  by  the  concrete 
and  by  the  steel  is  in  direct  ratio  to  the  relative  moduli  of  elasticity 
of  the  two  materials,  the  ratio  between  them  being  from  10  to  18; 
that  is,  steel  is  10  to  18  times  as  elastic  as  concrete,  or  will  carry  10 
to  1 8  times  the  load  with  the  same  amount  of  deformation.  The 
whole  secret  of  the  successful  design  of  reinforced  concrete  lies  in 
distributing  the  steel  in  such  positions  and  quantities  as  to  relieve 
the  concrete  of  any  pull  or  tension  as  well  as  any  excessive  shearing 
or  cutting  stresses,  and  leave  it  to  resist  the  crushing  stresses  which 
it  is  so  well  able  to  do. 

The  rigidity  of  a  reinforced  concrete  structure  arises  from  the 
fact  that  each  part  of  the  structure  is  inseparably  bound  to  every 
other  part  by  a  continuous  network  of  beams,  rods,  and  pillars,  and 
the  structure  is  one  whole  unit  and  not  a  collection  of  parts.  The 
monolithic  nature  of  these  structures  reduces  the  vibration  caused 
by  machinery  and  external  shocks,  and  has  proved  the  best  type  of 
construction  in  earthquake  countries,  and  where  unequal  settle- 
ment would  be  dangerous. 

The  durability  and  permanence  of  reinforced  concrete  arises 
from  the  very  nature  of  the  constituent  materials.  The  concrete 
becomes  stronger  as  times  goes  on,  and  the  steel  is  protected  from 
rusting  by  its  concrete  envelope.  In  fact,  so  great  is  this  protection 
that  painting  of  steel  work  is  very  objectionable  while  on  the  other 
hand  a  little  initial  rust  does  no  harm.  Abundant  experience  proves 
that' such  rust  is  removed  by  some  little  understood  chemical  process 
and  in  good  concrete  the  steel  will  always  remain  bright  and  clean. 
Special  advantages  appertaining  to  individual  structures  will  be 
discussed  in  appropriate  chapters. 

Materials  for  Reinforced  Concrete. — As  reinforced  concrete  is 
generally  used  where  strength  and  stiffness  are  required,  it  is  essential 

[167] 


Handbook  for  Cement  and  Concrete  Users 

that  a  rich  mixture  of  Portland  cement  be  employed  and  that  sand 
be  well  graded  and  clean. 

In  massive  work,  the  coarse  aggregate  may  run  as  high  as  2  1/2 
inches  in  size,  as  in  foundations  and  large  piers.  In  columns, 
girders,  beams,  and  slabs,  no  stone  or  other  aggregate  should  be 
used  larger  than  what  will  pass  a  one-inch  screen.  In  important 
beams  and  columns,  especially  when  the  reinforcing  bars  are 
closely  spaced,  the  size  should  be  made  even  smaller.  Good  trap 
rock  or  gravel  should  preferably  be  used. 

The  best  proportions  for  the  materials  which  enter  into  the 
concrete  depend  upon  the  size  and  character  of  the  construction. 
With  proper  limits  on  the  size  of  the  aggregate  and  with  coarse  sand 
containing  a  percentage  of  fine  grains,  a  mixture  of  one  part  of 
Portland  cement,  two  parts  sand,  and  four  parts  of  stone  or  gravel 
is  always  reliable. 

For  reinforced  concrete  work,  no  mixture  should  be  used  that 
does  not  develop  a  strength  of  at  least  2,000  Ibs.  per  sq.  in.,  in 
compression  at  the  age  of  28  days. 

It  is  not  the  province  of  this  book  to  go  into  the  higher  intricate 
details  of  the  design  of  reinforced  concrete  as  the  subject  is  com- 
plicated at  best,  and  the  reader  must  be  referred  to  the  many  ex- 
cellent treatises  on  design  now  to  be  had.  It  is  well  to  state,  how- 
ever, that  the  whole  subject  of  design  resolves  itself  into  the  study 
of  a  few  elementary  types  of  structure  such  as  the  beam  or  girder, 
the  slab,  the  column,  and  the  arch  and  all  structures,  however  com- 
plicated, are  either  a  modification  or  a  combination  of  these  element- 
ary types;  in  fact,  the  slab  is  even  a  modification  of  the  beam,  being 
a  beam  supported  on  all  sides.  The  amount  of  bending  or  other 
forces  produced  by  external  loading  is  computed  in  the  same  way 
as  in  any  other  structure,  the  problem  in  reinforced  concrete  being 
to  distribute  the  resultant  stresses  in  such  a  manner  between  the 
concrete  and  steel  as  to  have  the  concrete  take  the  compressive 
stresses  and  the  steel  take  the  tensile  stresses,  and  thus  require  the 
least  amount  of  each  material.  How  this  is  done  is  explained  in 
the  two  chapters  following. 


168] 


CHAPTER  XVII 

HOW  TO   DESIGN  REINFORCED   CONCRETE   BEAMS, 
SLABS,  AND  COLUMNS 

* 

Nature  of  the  Problem. — Kinds  of  Stresses. — Rules  for  Designing  Beams. — Rules  for 
Designing  Slabs. — Tables  for  Designing. — Solution  of  Examples. — Summary  of 
Procedure  in  Design. — Design  of  Reinforced  Concrete  Columns. — Examples  and 
Solution. 

Nature  of  the  Problem. ^Concrete  and  reinforced  concrete 
structures  when  called  upon  to  sustain  loads  or  pressures,  are 
thrown  into  a  state  of  stress.  When  the  loads  are  within  the  safe 
carrying  capacity  of  the  material,  this  condition  of  stress  is  shown 
by  a  slight  increase  or  diminution  in  size.  When  the  loads  exceed 
this  limit  the  material  is  no  longer  able  to  withstand  the  internal 
stress  and  the  structure  cracks,  ruptures,  or  exhibits  other  signs  of 
failure. 

In  order  to  properly  design  a  concrete  structure,  it  is  necessary 
to  make  an  investigation  to  determine  whether  or  not  the  material 
is  so  disposed  as  to  be  able  to  withstand  the  effects  of  the  external 
loads  without  on  the  one  hand  being  stressed  beyond  the  point  of 
safety,  or  on  the  other  hand  without  waste  of  material. 

Such  an  investigation  should  comprise  the  following  operations: 

(1)  Determination  of  the  amount  and  position  of  the  external 
loads,  including  the  weight  of  the  structure  itself. 

(2)  Determination  of  the  kind,  amount,  and  position  of  the 
greatest  internal  stress  produced  by  such  loads. 

(3)  Determination  of  the  resisting  power  of  the  material  to 
withstand  such  an  internal  stress. 

Kinds  of  Stress. — According  to  the  position  of  the  external  loads 
a  body  may  be  called  upon  to  sustain  one  or  more  of  the  following 
kinds  of  stress : 

(i)  Tension;   (2)  Compression;   (3)  Shear;   (4)  Bending. 

[169] 


Handbook  for  Cement  and  Concrete  Users 

A  body  is  subjected  to  tension  or  is  under  a  tensile  stress  when 
acted  upon  by  forces  which  tend  to  tear  or  pull  it  apart,  as  a  stretched 
rope. 

A  body  is  under  compression  or  undergoes  a  compressive  stress 
when  the  external  forces  tend  to  crush  the  material  of  which  it  is 
composed  as  a  bridge  abutment  or  pier. 

A  body  is  subjected  to  shear  or  is  under  a  shearing  stress  when 
acted  upon  by  forces  which  tend  to  cut  or  shear  it  across,  as  the 
rivets  in  a  boiler  tube,  when  the  overlapping  edges  of  the  tube  tend 
to  slide  apart  under  the  action  of  the  internal  pressure. 

A  body  is  subjected  to  bending  when  used  as  a  beam  or  girder  to 
carry  a  load  over  an  opening.  This  action  is  illustrated  in  the  case 
of  a  plank.  When  a  plank  is  laid  flatwise  and  supported  at  the 
ends,  a  comparatively  slight  load  at  the  centre  will  cause  it  to  sag  or 
bend.  The  effect  of  this  bending  is  to  compress  the  material  in  the 
upper  surface  of  the  plank  and  to  stretch  the  material  in  the  lower 
surface.  Between  these  surfaces,  there  is  a  plane  which  is  neither 
compressed  nor  lengthened.  Such  a  plane  is  called  the  neutral 
surface. 

A  plank  laid  flatwise  makes  a  very  weak  beam,  because  of  the 
excessive  bending.  When  set  up  on  edge,  a  plank  is  far  stiffer 
and  stronger.  Nevertheless,  such  a  joist  tends  to  sag  at  the  centre, 
so  that  the  upper  surface  is  in  compression  and  the  lower  surface  in 
tension,  but  the  amount  of  sag  or  deflection  is  slight  compared  with 
what  it  would  be  were  the  plank  turned  on  its  broad  side. 

Both  plain  and  reinforced  concrete  is  used  in  columns,  piers, 
foundations,  walls,  etc.,  where  it  is  subjected  to  a  compressive  stress. 

Reinforced  concrete  is  also  employed  in  beams,  slabs,  and  other 
structures  which  are  subjected  to  a  bending  stress,  the  steel  being 
so  disposed  as  to  take  care  of  the  tension  in  the  lower  part  of  the 
beam  or  slab. 

Concrete  is  never  employed  in  direct  tension  for  carrying  a 
suspended  load,  as  steel  is  far  lighter  and  more  economical  for  the 
purpose. 

Action  of  Steel  and  Concrete  in  Combination. — When  steel  rods 
are  embedded  in  concrete,  the  adhesion  between  the  steel  and 
concrete  is  practically  equal  to  the  bond  between  the  ingredients 
(cement,  sand,  and  stone)  of  which  the  mixture  is  composed.  In 

[170] 


Horizontal  reinforcement  only.  Method  of  failure  when  tested  to  destruction. , 
L>ight  load.  Sudden  failure  caused  by  ends  of  reinforcement  slipping  and 
•orizontal  shear  diagonal  cracks  in  concrete. 


zfitKirasx*'* 

no  diagonal  cracks. 


A-ch  action  in  beam  with  horizontal  reinforcement  and  stirrups.  Note  the 
unbalanced  horizontal  stress.  Stirrups  slip  along  the  horizontal  reinforcement, 
which,  therefore,  cannot  be  developed. 


Beam  with  horizontal  reinforcement  only.      Note  arch  action.      Reinforcement 
furnishes  no  abutment  for  the  inclined  stresses,  and  will  slip. 


Truss  action  in  beam  reinforced  with  Kahn  Trussed  Bars.     Note  the  actio 
that  of  a  complete  Pratt  truss      No  tendency  to  slip  or  slide. 


/A  ^ 

Truss  action  in  beam  with  horizontal  reinforcement  and  stirrups.     Note  th« 

unbalanced  horizontal  component  of  the  inclined  stress  and  the  tendency  of  th« 

Stirrups  to  slip  along  the  horizontal  reinforcement 


Arch  action  in  beam  reinforced  with  Kahn  Trussed  Bars.     Note  the  perfect 
abutment  for  t:.e  inclined  stresses.,  _Perfectljr  rigid  and  no  possibility  of  slipping. 


Kahn  reinforcement.     Method  of   failure  when   tested   to  destruction.     Max- 
imum  load.     Very  gradual  and  ideal  tailure.     Steel  stretching  in  center. 

FIG.  48. — Sketches  Showing  Failure  of  Concrete  Beams  Reinforced  in  Different  Ways, 
When  Tested  to  Destruction.     (Kahn.) 


Handbook  for  Cement  and  Concrete  Users 

general  for  ordinary  round  or  square  bars,  the  bond  strength  may 
be  taken  -at  from  200  to  300  Ibs.  per  sq.  in.  of  surface,  and  for 
indented  bars,  having  in  addition  a  mechanical  bond,  at  from  300 
to  500  Ibs.  per  sq.  in.  These  are  breaking  strains,  and  for  the 
purpose  of  safe  design,  the  bond  strength  is  considered  to  be  only 
50  to  75  pounds  per  sq.  in.  of  steel  surface. 


^7!f^^  j 


FIG.  49. — Test  of  Girder  under  Load  with  and  without  Stirrups.      (Hennebique.) 

Steel  and  concrete  also  expand  at  practically  the  same  rate  when 
heated,  so  that  change  of  temperature  does  not  cause  any  tendency 
for  the  steel  to  slip  or  separate  from  the  concrete. 

Action  of  Steel  and  Concrete  in  Sustaining  Stress. — When  a 
reinforced  concrete  member  is  subjected  to  stress,  as  for  example, 
a  column  or  post  containing  vertical  rods,  the  stress  will  be  divided 


How  to  Design  Reinforced  Concrete 

between  the  steel  and  concrete  in  direct  proportion  to  the  ability 
of  each  to  carry  the  load.  Steel,  as  already  stated,  is  said  to  have 
a  modulus  of  elasticity  from  10  to  18  times  as  great  as  that  of  con- 
crete, which  means  that  the  steel  rods  in  a  column  will  carry  from 
10  to  1 8  times  as  much  stress  per  sq.  in.  of  cross-section  as  the 
surrounding  concrete.  The  reason  of  this  is  that  the  loads  on  a 
column  tend  to  shorten  it,  and  from  10  to  18  times  as  much  weight 
is  required  to  shorten  a  steel  column  by  a  given  amount  as  is  needed 
to  compress  a  concrete  column  having  the  same  dimensions  by 
an  equal  amount. 

Effect  of  Spiral  Wrappings. — Posts  are  frequently  reinforced 
with  spiral  bands  or  hoops  as  well  as  with  vertical  rods.  Such 
wrappings  do  not  support  any  part  of  the  load  directly.  Their 
object  is  to  increase  the  bearing  power  of  the  concrete  by  preventing 
lateral  expansion  or  bulging  under  the  action  of  the  compressive 
forces.  Tests  published  by  Considere  in  1903  indicate  that  steel 
in  the  form  of  spiral  reinforcements  is  2.4  times  as  efficient  as  in 
the  form  of  longitudinal  rods,  provided  the  spacing  of  the  wire  is 
not  too  great  (1/4  to  i/io  of  the  diameter  of  the  spiral).  The 
chief  effect  of  hooping  is  to  increase  the  toughness  or  ductility  of 
the  concrete,  which  is  desirable  on  account  of  the  comparatively 
brittle  nature  of  the  column  with  longitudinal  reinforcement  only. 

In  hooped  columns  only  that  portion  of  the  concrete  which  is 
within  the  spirals  can  be  regarded  as  bearing  any  part  of  the  load. 
When  so  regarded,  and  when  the  wrapping  is  circular  in  form  and 
the  reinforcement  sufficient  to  insure  a  lateral  resistance  of  at  least 
65  pounds  per  square  inch,  the  hooping  can  be  considered  as  in- 
creasing the  bearing  capacity  of  the  concrete  by  50  per  cent. 

DESIGN    OF    SIMPLE    BEAMS   AND    SLABS   CARRYING 
''UNIFORMLY  DISTRIBUTED  LOADS"    . 

V 

While  the  design-  of  a  reinforced  concrete  structure  requires 
both  a  working  knowledge  of  the  mechanics  of  materials,  and 
practical  experience  with  the  constructor's  side  of  the  art,  it  is 
nevertheless  feasible  for  anyone  with  a  little  practice  to  compute 
the  dimensions  of  simple  beams  and  slabs. 

Simple  beams  are  beams  which  are  supported  at  each  end. 


Handbook  for  Cement  and  Concrete  Users 

Continuous  girders  have  one  or  more  intermediate  supports.  In 
simple  horizontal  beams  the  steel  is  placed  near  the  bottom  at  the 
centre  of  the  span  and  part  of  the  bars  are  bent  up  near  the  ends 
and  anchored  over  the  supports  by  bending.  If  the  beam  is  con- 
tinuous the  bent  rods  stop  at  the  top,  and  in  addition  a  system  of 
horizontal  rods  is  placed  in  the  upper  part  of  the  beam  and  these 
extend  over  the  supports  to  the  quarter  points. 

Stirrups  are  also  employed  in  both  simple  and  continuous  girders, 
especially  when  the  loads  are  heavy  in  proportion  to  the  span.  The 
proper  placing  of  the  steel  and  its  anchorage  at  the  supports  are 
just  as  important  as  is  the  computation  of  loads  and  stresses.  In 
this  chapter  simple  practical  formulas  are  given  for  determining 
the  proper  size  of  simple  beams  and  the  amount  of  steel  required 
for  their  reinforcement.  They  can  be  used  for  continuous  girders, 
only  when  proper  provision  is  made  for  the  placing  of  steel  over 
the  supports,  at  the  top  of  the  beams. 

The  percentage  of  steel  required  for  a  reinforced  concrete  girder 
is  generally  a  little  less  than  one  per  cent.  Perhaps  the  most 
economical  percentage  is  seven-tenths  of  one  per  cent.  This 
applies  to  the  main  steel  bars  in  the  bottom  of  the  beam.  The 
steel  employed  for  stirrups  and  the  horizontal  rods  at  the  top  of 
continuous  girders  are  not  included  in  this  percentage. 

The  load  carried  by  a  reinforced  concrete  girder  is  generally 
considered  to  be  uniformly  distributed  over  its  length.  This  applies 
to  girders  which  support  floor  slabs,  and  to  the  general  run  of 
factory  construction.  It  does  not  apply  to  a  girder  carrying  a 
heavy  machine  at  the  centre  of  the  span. 

Points  to  be  Considered  in  the  Design. — The  rational  design  of 
beams  and  slabs  of  reinforced  concrete  involves  the  study  of  the 
features  enumerated  below.  For  complete  analysis  of  all  these 
points  reference  must  be  had  to  special  works  on  Reinforced  Con- 
crete Design.  We  give  below  in  this  chapter  the  rules  and  formulas 
for  such  design  reduced  to  the  simplest  forms  for  practical  use, 
and  in  the  succeeding  chapter  the  origin  and  explanation  of  these 
formulas  are  discussed  for  those  who  wish  to  study  the  theory  as 
well  as  the  practical  applications  of  the  formulas.  The  following 
data  *  are  usually  considered  in  the  design : 

*  From  "  Concrete  in  Factory  Construction,"  by  the  Atlas  Portland  Cement  Co. 

[174] 


How  to  Design  Reinforced  Concrete 

"  (i)  The  bending  moment  due  to  the  live  and  dead  loads,  this 
involving  the  selection  of  the  proper  formula  for  the  computation. 

"  (2)  Dimensions  of  beams  which  will  prevent  an  excessive 
compression  of  the  concrete  in  the  top,  and  which  will  give  the 
depth  and  width  which  is  otherwise  most  economical. 

"  (3)  Number  and  size  of  rods  to  sustain  tension  in  the  bottom 
of  the  beam. 

"  (4)  Shear  or  diagonal  tension  in  the  concrete. 

"  (5)  Value  of  bent-up  rods  to  resist  shear  or  diagonal  tension. 

"(6)  Stirrups  to  supplement  the  bent-up  rods  in  assisting  to 
resist  the  shear  or  diagonal  tension. 

"  (7)  Steel  over  the  supports  to  take  the  tension  due  to  negative 
bending  moments. 

"  (8)  Concrete  in  compression  at  the  bottom  of  the  beam  near 
the  supports  due  to  negative  bending  moment. 

"  (9)  Horizontal  shear  under  flange  of  slab. 

"  (10)   Shear  on  vertical  planes  between  beams  and  flanges. 

"(n)   Distance  apart  of  rods  to  resist  splitting. 

"  (12)  Length  of  rods  to  prevent  slipping. 

"  (13)   End  connections  at  wall." 

Rules  for  Designing  Beams. — In  a  horizontal  reinforced  concrete 
beam  carrying  a  uniformly  distributed  load,  the  proper  dimensions 
may  be  obtained  from  the  following  formula,  which  is  based  on  the 
straight -line  theory  of  stress  as  explained  in  the  next  chapter: 

bd2=ysi(w  +  w>) 

74 
and  the  sectional  area  of  steel  required  in  the  lower  portion  of  the 

beam  by  the  formula : 

A  =  .007  b  d (2) 

Where  b  denotes  the  breadth  of  the  beam  in  inches,  d  denotes 
the  depth  in  inches  from  the  top  or  compressive  face  of  the  beam 
to  the  plane  of  the  steel. 

/  =  the  length  of  span  in  inches. 

W  =  the  external  load  on  the  beam  in  pounds  and  includes  the 
weight  of  the  floor  slab  which  is  supported  by  the  beam. 

W  =  the  estimated  weight  of  the  beam  itself  in  pounds. 

A  =  the  sectional  area  of  the  steel  in  square  inches. 

p  =  the  percentage  of  steel. 

h75] 


Handbook  for  Cement  and  Concrete  Users 


The  above  formulas  are  based  on  seven-tenths  of  one  per  cent 
of  steel  being  employed  for  reinforcement  in  the  bottom  flange. 
If  other  proportions  of  steel  are  employed,  the  same  formulas  can 
be  used  by  changing  the  denominator  from  74  to  the  appropriate 
value  as  shown  in  the  following  table.  This  table  is  based  on' a 
maximum  compressive  stress  in  the  concrete  of  500  pounds  per  sq. 
in.,  a  ratio  of  12  between  the  modulus  of  elasticity  of  concrete  and 
that  of  steel,  and  a  tensile  stress  in  the  steel  ranging  from  15,000  to 
8,000  Ibs.  per  sq.  in.,  according  as  the  percentage  of  steel  is  low  or 
high. 

TABLE  XVI. — DENOMINATORS  FOR  USE  IN  FORMULA  I.  FOR 
DIFFERENT  PERCENTAGES  OF  STEEL.* 


Percentage  of 

Steel,  p  

.005 

.606 

.007 

.008 

.009 

.010 

-Oil 

.012 

.013 

.014 

.015 

Denominator 

for  formula  (i)  . 

66 

70 

74 

78 

81 

84 

86 

89 

91 

93 

95 

Thus  if  one  per  cent  of  steel  is  desired,  the  formulas  become : 

/  (W  +  W) 


bd2  = 


and 


84 


.010  b  d 


(3) 


(4) 


Example.  —  Compute  the  dimensions  of  a  horizontal  reinforced 
concrete  beam,  which  can  be  used  to  support  a  uniformly  distributed 
load  of  15,000  pounds,  including  the  weight  of  the  floor  slab,  over 
a  span  of  14  feet. 

Solution.  —  An  economical  value  for  p  is  .007;  W  =  15,000  Ibs. 
Assume  W  —  5,000  Ibs.,  I  =  14  X  12  =  168  inches.  Hence  sub- 
stituting in  formula  (i)  we  have: 

772  _  y%  X  1  68  (15000+  5000)        420000 

74  74 

Assume  any  practicable  width  for  b,  as  b  =  13  inches,  then, 


5676 


=  436.6 


*  The  derivation  of  Table  XVI.  is  given  in  Chap.  XVIII. 
[176] 


How  to  Design  Reinforced  Concrete 

and  solving  for  d,  which  may  be  facilitated  by  the  use  of  a  table  of 
squares,  we  have: 

d  =  21  inches 

A  =  .007  X  13  X  21  =  1.911  sq.  ins. 

If  the  1.911  sq.  ins.  is  divided  among  4  rods,  the  area  of  each  will 
be  1.911  •*-  4  =  0.478  sq.  ins. 

If  square  rods  are  employed,  the  required  dimensions  will  be 

4-11/16  inch  rods,  since  11/16  X  11/16  =  0.478  (nearly) 

d  =  21  inches  is  the  effective  depth  or  depth  to  the  plane  of  the 
steel.  At  least  2  inches  of  concrete  should  be  placed  below  the 
steel  for  protection  and  bond.  Hence  the  total  depth  of  .the  beam 
must  be  21  +2  =23  inches. 

If  a  heavy  rock  concrete  weighing  144  pounds  per  cu.  ft.,  in- 
cluding the  steel,  is  employed,  the  weight  of  the  beam  23  ins.  deep, 
13  ins.  wide,  and  14  feet  long,  will  be 

^3x^xHx!44x  =  4>l86  pounds. 

12  12  I  I 

This  is  814  pounds  less  than  the  assumed  weight,  and  if  the  dimen- 
sions are  again  computed,  using  the  actual  weight  of  4,186  pounds 
in  place  of  the  assumed  weight  of  5,000  pounds,  it  will  be  found  to 
make  a  difference  of  half  an  inch  in  the  required  depth  of  the  beam. 

An  inspection  of  the  above  computation  for  weight  reveals  a 
quick  method  for  obtaining  the  weight  of  heavy  rock  concrete; 
viz.,  multiply  together  the  total  depth  in  inches  by  the  breadth  in 
inches  by  the  length  of  the  beam  in  feet. 

The  above  method  of  designing  a  beam  will  probably  impress 
the  novice  as  faulty  in  that  too  much  is  assumed  in  advance.  A 
very  little  practice  will,  however,  enable  him  to  estimate  the  probable 
weight  very  much  more  closely  than  was  done  in  the  above  example, 
where  the  beam  was  purposely  overestimated  by  20  per  cent  in 
order  to  show  that  such  an  overestimate  has  very  little  effect  on  the 
design,  and  even  if  the  first  estimate  should  be  extremely  wide  of 
the  mark,  two  trials  at  the  most  should  be  all  that  would  be  required 
to  determine  the  proper  dimensions. 

In  assuming  the  percentage  of  lower  flange  steel  in  advance, 
the  designer  has  two  things  to  consider;  first  the  most  economical 
12  [177] 


Handbook  for  Cement  and  Concrete  Users 

percentage;  and  second,  whether  he  wishes  to  make  the  com- 
pression or  tension  half  of  his  beam  the  stronger.  Probably  .007 
is  the  most  economical  percentage,  as  less  than  this  amount  of  steel 
unduly  increases  the  volume  of  concrete,  while  more  than  .007 
affects  unfavorably  the  cost  of  the  steel.  Below  .01  the  steel  will 
probably  be  weaker  than  the  concrete  at  a  breaking  load,  while 
above  .01  the  steel  is  likely  to  prove  the  stronger.  Near  this  point 
either  the  steel  or  the  concrete  may  be  the  first  to  fail  if  the  beam  is 
tested  to  destruction,  depending  chiefly  on  the  materials  and  work- 
manship employed  in  mixing  and  placing  the  concrete.  The 
designer  should  be  sufficiently  familiar  with  the  quality  of  the  work 
so  that  he  can  fix  the  percentage  of  steel  at  such  a  rate  that  the  steel 
will  begin  to  stretch  before  the  concrete  commences  to  crumple, 
thus  producing  deflection  and  giving  warning  in  advance,  in  case 
the  beam  should  be  loaded  beyond  its  capacity.  In  addition  to  this 
percentage,  upper  flange  steel  over  the  supports  and  stirrups  should 
in  general  be  provided. 

In  assuming  the  breadth  and  computing  the  effective  depth, 
after  the  design  has  reached  the  stage  where  the  product  b  d2  =  a 
known  number,  several  trials  may  be  necessary  to  give  the  best 
proportions  for  the  beam.  For  economy  a  beam  is  made  as 
narrow  as  possible,  but  there  are  practical  limits  to  decreasing 
the  breadth  which  must  not  be  encroached  upon.  Thus  a 
beam  should  not  be  narrower  than  1/24  of  the  span.  It  must 
be  wide  enough  to  provide  at  least  i  1/2  diameters  and  prefer- 
ably 2  between  the  reinforcing  bars  and  between  the  bars 
and  sides  of  the  beam.  Moreover,  the  breadth  should  not  be 
less  than  half  of  the  depth,  excepting  for  very  large  beams. 
Probably  the  best  width  is  between  1/2  and  3/4  of  the  effective 
depth,  d. 

How  to  Design  Reinforced  Concrete  Slabs.— For  the  purpose 
of  design,  a  reinforced  concrete  slab  placed  as  a  continuous 
sheet  over  several  girders  and  carrying  a  uniformly  distributed 
load,  may  be  treated  as  though  the  slab  was  divided  into  nar- 
row strips,  each  having  a  width  equal  to  the  spacing  of  the 
reinforcing  bars,  and  a  length  equal  to  the  distance  between  the 
supporting  girders. 

The  slab  can  then  be  designed  by  the  following  formulas: 


How  to  Design  Reinforced  Concrete 

(W  +  W>)  ' 

74 
A  =  .007  b  d (6) 

Formulas  (5)  and  (6)  are  identical  in  form  with  those  employed 
for  beams,  and  differ  only  in  the  coefficient  of  /,  i/io  being  used 
instead  of  1/8.  The  nomenclature  is  also  the  same,  and  if  a  per- 
centage of  steel  different  from  .007,  is  desired,  the  corresponding 
denominator  for  formula  (5)  can  be  obtained  from  Table  XVI  in  the 
same  way  as  for  beams.  Such  a  slab  requires  top  reinforcement 
extending  over  the  girders  for  at  least  one-fourth  of  the  span,  on 
both  sides  of  the  girder;  or  if  expanded  metal  or  other  fabric  is 
employed  the  fabric  must  be  placed  so  that  in  the  centre  of  the  span  it 
will  sag  to  near  the  bottom  of  the  slab,  while  over  the  supports  it 
will  be  near  the  top.  The  sectional  area  of  lower  flange  steel  may 
be  obtained  from  formula  (6),  when  seven-tenths  per  cent  is  used, 
or  the  coefficient  .007  may  be  varied  to  suit  the  requirements. 

Example. — Design  a  reinforced  concrete  slab  supported  by 
beams  spaced  8  feet  apart,  which  may  be  used  to  sustain  a  uniform 
load  of  125  pounds  per  square  foot,  exclusive  of  its  own  weight. 

Solution. — Assume  a  steel  percentage  of  .007,  a  spacing  of  the 
reinforcing  bars  of  6  inches;  and  the  weight  of  a  strip  6  inches  wide, 
and  8  feet  long  at  240  pounds. 

By  spacing  the  bars  6  inches  apart,  the  breadth,  6,  becomes 
6  inches,  and  the  external  load,  W,  at  125  pounds  per  sq.  ft.,  will  be: 

W  =  8  ft.  X  6/i2  ft.  X  125  Ibs.  per  sq.  ft.  =  500  pounds 

while 

/  =  8  X  12  =  96  inches. 

Substituting  in  formula  (5)  we  have : 

i/ioX  96  (500  +  240) 
o  a   =  -+r  • 

74 

d2  =  1 6  sq.  ins. 

d   =  4  ins.  depth  to  the  plane  of  the  steel. 

If  i  inch  of  concrete  is  placed  below  the  steel,  the  required  thickness 
of  the  slab  will  be  4  +  i  =  5  inches. 

[179] 


Handbook  for  Cement  and  Concrete  Users 

From  (6)  the  area  of  steel  will  be 

A  =  .007  X  4  X  6  =  .168  sq.  ins. 

This  may  be  obtained  from  1-1/2  inch  round  rod. 

When  fabric  is  employed  instead  of  steel  rods,  a  strip  i  foot  wide 
is  taken  as  the  basis  of  the  design,  or  b  =  12  inches,  while  formula 
(6)  will  give  the  sectional  area  of  fabric  required  for  the  i-foot  strip, 
for  seven-tenths  per  cent  of  steel. 

In  general,  a  reinforced  concrete  slab  should  not  be  less  than  3 
inches  thick  and  should  have  at  least  3/4  inch  of  concrete  below  the 
steel. 

In  an  oblong  slab  the  steel  is  placed  crosswise  from  girder  to 
girder.  In  a  square  slab  supported  on  four  girders,  equidistant 
from  each  other,  the  rods  are  placed  both  ways.  When  reinforced 
in  this  manner,  the  same  amount  of  steel  is  used»as  for  the  oblong 
slab,  but  there  is  a  saving  in  concrete,  as  the  concrete  for  a  square 
slab  need  only  be  designed  for  half  the  load. 

In  an  oblong  slab,  a  few  rods  should  also  be  placed  longitudinally 
to  prevent  temperature  cracks  and  to  serve  as  binders  for  the  main 
tension  bars  which  run  crosswise  between  the  supporting  girders. 

Tables  for  Use  in  Designing  Beams  and  Slabs. — Such  tables 
may  be  divided  into  two  classes:  (a)  those  which  give  the  required 
dimensions  without  computation,  and  (b)  those  which  are  used  to 
facilitate  computation  by  saving  arithmetical  labor.  Tables  XVII, 
XVIII,  and  XIX  are  of  the  latter  and  Table  XX  of  the  former  class. 

Table  XVII  is  a  table  of  squares  for  facilitating  the  computation 
of  beam  depths.  Table  XVIII  gives  the  weight  per  lineal  foot  of  re- 
inforced concrete  beams  at  144  pounds  per  cubic  foot,  and  is  used 
for  estimating  the  weight  of  beams.  Table  XVIII  also  shows  com- 
parative costs  of  beams  at  $10.00  per  cu.  yd.  This  is  for  the  purpose 
of  comparing  the  cost  of  beams  of  different  proportions  of  depth  to 
breadth  and  of  different  percentages  of  steel,  in  order  to  employ 
those  which  are  most  economical.  Table  XIX  gives  the  sectional 
areas  of  round  and  square  bars,  and  their  weights  and  cost  at  the 
rate  of  2  cents  per  pound.  This  is  also  convenient  for  making  a 
comparison  of  costs.  The  costs  given  in  Tables  XVIII  and  XIX  do 
not  represent  the  actual  costs,  which  may  be  50  per  cent  more  or  less 
for  any  given  structure.  They  are  relative  costs  for  gauging  the 

[180] 


How  to  Design  Reinforced  Concrete 

relative   economy   of   different   beams   having   equal   strength  or 
capacity. 

Table  XX,  which  is  reproduced  with  slight  modifications,  by 
courtesy  of  the  Atlas  Portland  Cement  Co.,  from  their  book  on 
the  utilization  of  "Concrete  in  Factory  Construction/'  gives  the 
proper  dimensions  for  beams  and  slabs  that  will  carry  uniformly 
distributed  floor  or  roof  loads  of  125,  50,  and  30  pounds  respectively, 
per  square  foot.  These  beams,  if  checked  over,  by  the  straight  line 
formulas  (10)  and  (u),  of  Chapter  XVIII,  will  be  found  to  average 
about  seven-tenths  per  cent  of  steel,  to  have  a  fibre  stress  in  the 
concrete  of  about  500  pounds  per  square  inch,  and  in  the  steel  of 
between  12,000  and  15,000  pounds  per  square  inch. 


TABLE  XVII.— BEAM  DEPTHS  AND  THEIR  SQUARES. 


No. 

Square. 

No. 

Square. 

No. 

Square. 

No. 

Square. 

No. 

Square. 

No. 

Square. 

2.00 

4.00 

5.00 

25  -00 

8.00 

64.00 

12  .00 

144.00 

18.00 

324.00 

24.00 

576.00 

2.25 

5.06 

5-25 

27.56 

8.25 

68.06 

12  .50 

156-25 

18.50 

342.25 

24.50 

600.25 

2.50 

6.25 

5-50 

30-25 

8.50 

72.25 

13  .OO 

169.00 

19.00 

361  .00 

25  .00 

625.00 

2-75 

7-56 

5-75 

33-06 

8-75 

76.56 

I3-50 

182  .25! 

19.50 

380.25 

25  -5° 

650.25 

3.00 

9.00 

6.00 

36.00 

9.00 

81.00 

14.00 

196.00 

20.00 

400.00 

26.00 

676.00 

3-25 

10.56 

6.25 

39  -.06; 

9-25 

85-56 

14.50  210.25 

20.50 

420.25 

26.50 

702.25 

3-50 

12.25 

6.50 

42.25 

9-50 

90.25 

15.00 

225  .00 

21  .OO 

441  .00 

27  .00 

729.00 

3-75 

14.06 

6-75 

45-56, 

9-75 

95.06 

I5-50 

240.25 

21  .50 

462.25 

27.50 

756.25 

4.00 

16.00 

7.00 

49-0° 

10.  OO 

100.00 

16.00 

256.00 

22  .OO 

484.00 

28.00 

784.00 

4-25 

18.06 

7-25 

52-56 

10.50 

110.25 

16.50 

272.25 

22  .50 

506.25 

28.50 

812.25 

4-5° 

20.25! 

7-50 

56-25 

II  .00 

121  .OO 

17  .00 

289  .00 

23.00 

529.00 

29.00 

841.00 

4-75 

22  .56 

7-75 

60.06 

II  .50 

132-25 

I7-50 

306-25 

23-50 

552-25 

29.50 

870.25 

Example,  Involving  Use  of  Tables. — Compute  the  cost  of  beams 
spaced  8  feet  apart,  and  having  a  span  of  12  feet  which  will  support 
a  6-inch  slab  of  concrete  in  addition  to  a  floor  load  of  140  pounds 
per  square  foot. 

Solution. — Surface  area,  12  X  8  =  96  sq.  ft.  Load  96  X  140  = 
I3,44olbs. 

Weight  of  slab  12  X  8  X  --  X  144  Ibs.  per  cu.  ft.  =  6,912  Ibs. 

Estimated  weight  of  beam,  Table  XVIII,  12  x  24  ins.  (288  X  12) 
=  3,456  Ibs.  13,440  +  6,912  +  3,456  =  23,808  Ibs. 

[181] 


Handbook  for  Cement  and  Concrete  Users 


TABLE  XVIII. 

Weight  of  Heavy  Reinforced  Concrete  Beams  in  Pounds  per  Lineal  Foot,  also  Cost 
of  the  Concrete  in  Dollars  per  Lineal  Foot  at  the  Rate  of  $10.  oo  per  Cubic  Yard. 


BREADTH  IN  INCHES. 

4 

5 

6 

7 

8 

9 

10 

12 

14 

16 

"[ 

,j 

12 

15 

18 

21 

24 

27 

30 

36 

42 

48 

54 

Weight 

3i 

.031 

•039 

.046 

•054 

.062 

.070 

.077 

•093 

.108 

.124 

•139 

Cost 

j 

16 

20 

24 

28 

32 

36 

40 

48 

56 

64 

72 

Weight 

41 

.041 

.052 

.062 

.072 

•083 

•093 

.103 

.124 

.144 

.165 

.185 

Cost 

-  j 

20 

25 

3° 

35 

40 

45 

5° 

60 

7° 

80 

90 

Weight 

51 

.052 

.065 

.077 

.090 

.103 

.116 

.129 

•155 

.180 

.206 

.232 

Cost 

6 

24 

30 

36 

42 

48 

54 

60 

72 

84 

96 

108 

Weight 

I 

.062 

.077 

•093 

.108 

.124 

•J39 

•155 

.185 

.216 

•247 

.278 

Cost 

7^ 

28 

35 

42 

49 

56 

63 

70 

84 

98 

112 

126 

Weight 

M 

.072 

.090 

-.108 

.126 

.144 

.162 

.180 

.216 

.252 

.288 

•324 

Cost 

gj 

32 

40 

48 

56 

64 

72 

80 

96 

112 

128 

144 

Weight 

1 

.083 

.103 

.124 

.144 

•165 

•185 

.206 

.247 

.288 

•33° 

•371 

Cost 

OJ 

36 

45 

54 

63 

72 

81 

90 

108 

126 

144 

162 

Weight 

9! 

•093 

.116 

•*39 

.162 

-185 

.208 

.232 

.278 

•324 

•371 

.417 

Cost 

g 

H 

-  \ 

40 

5° 

60 

7° 

80 

90 

IOO 

120 

140 

1  60 

1  80 

Weight 

0 

fe 

I 

.103 

.129 

•J55 

.180 

.206 

.232 

•  257 

•309 

.360 

.412 

•463 

Cost 

fc 

12   J 

60 

72 

84 

96 

1  08 

120 

144 

1  68 

192 

216 

Weight 

H 

1 

•155 

.185 

.216 

.247 

.278 

•3°9 

•371 

•433 

•494 

•556 

Cost 

£ 

_.   J 

84 

98 

112 

126 

140 

1  68 

196 

224 

252 

Weight 

5 

U  1 

.216 

.252 

.288 

•  324 

.360 

•432 

•504 

.576 

.648 

Cost 

j 

•< 
bi 

i6J 

112 

128 

144 

1  60 

192 

224 

256 

288 

Weight 

1 

1 

.288 

•330 

•371 

.412 

•494 

•576 

•659 

.741 

Cost 

**\ 

144 

162 

1  80 

216 

252 

288 

324 

Weight 

1 

•371 

.417 

•463 

.556 

.648 

.741 

•834 

Cost 

20 

Weight  per  lineal  foot  = 

1  80 

200 

240 

280 

320 

360 

Weight 

1 

H 

Breadth  in  inches  multi- 
plied by  total  depth  in 
inches. 

•463 
198 
•509 

•515 
220 
.566 

.617 
264 
.679 

.720 
308 
•   793 

.823 

352 
.906 

.926 

396 
i  .019 

Cost 
Weight 
Cost 

•4  4 

240 

288 

336 

384 

432 

Weight 

41 

,6J 

Cost  in  dollars  at  $10.00  per  cu. 
yd.  =  weight    per   lineal  foot 

.617 

•741 
312 

.864 
364 

.988 
416 

i  .in 

468 

Cost 
Weight 

( 

multiplied  by  .002572. 

•803;    .936 

i  .070 

i  .204 

Cost 

28  J 

336 

392 

448 

504 

Weight 

1 

.865 

i  .009 

I-I53 

1.297 

Cost 

30  -! 

360 

420 

480 

540 

Weight 

I 

.926 

1.081 

1-235 

1.389 

Cost 

182 


How  to  Design  Reinforced  Concrete 
TABLE  XIX.— PROPERTIES  OF  STEEL  BARS. 


ROUND  BARS. 

SQUARE  BARS. 

Diameter 
in  Inches. 

Sectional 
Area  in 
Square 
Inches. 

Weight 
per 
Lineal 
Foot  in 
Pounds. 

Cost  in 
Dollars  per 
Lineal  Foot 
at  2  Cents 
per 
Pound. 

Circum- 
ference 
in 
Inches. 

Sectional 
Area  in 
Square 
Inches. 

Weight 
per 
Lineal 
Foot  in 
Pounds. 

Cost  in 
Dollars 
per 
Lineal  Foot 
at  2  Cents. 

Peri- 
meter 
in 
Inches. 

1/8 

.  .0123 

.042 

.001 

•  3927 

.0156 

•  053 

.001 

0.50 

3/1  6 

.0276 

.094 

.002 

.5890 

•  0352 

.120 

.002 

0-75 

i/4 

.0491 

.167 

.003 

•7854 

.0625 

.213 

.004 

I  .00 

5/i  6 

.0767 

.261 

.005 

.9817 

•  0977 

•  332 

.007 

1-25 

3/8 

.  1104 

•  376 

.008 

i  .  1781 

.  1406 

.478 

.010 

1.50 

7/i  6 

•  1503 

.511 

.010 

1-3744 

.1914 

.651 

.013 

i./S 

i/a 

.1963 

.668 

•  013 

i.57o8 

.2500 

.850 

.017 

2  .00 

0/16 

.2485 

.845 

.017 

i  .7671 

.3164 

.076 

.022 

2.25 

5/8 

.3068 

i  .043 

.021 

1-9635 

-39o6 

.328 

.027 

2.50 

i  '/i  6 

•  3712 

i  .  262 

.025 

2  .  1598 

.4727 

.607 

.032 

2-75 

3/4 

.4418 

i  .502 

.030 

2.3562 

•  5625 

•  913 

.038 

3  .00 

13/16 

•  5185 

i  .763 

•035 

2.5525 

.6602 

•  245 

•045 

3  -25 

7/8 

•  6013 

2.044 

.041 

2.7489 

.7656 

.603 

.052 

3  -50 

15/16 

.6903 

2-347 

•047 

2.9452 

.8789 

.989 

.  060 

3  -75 

•  7854 

2  .670 

•053 

3  .1416 

.  oooo 

3  -400 

.068 

4.00 

1    1/16 

.8866 

3-014 

.060 

3  -3379 

.  1289 

3-838 

.077 

4-25 

1/8 

.9940 

3-379 

.068 

3-5343 

.2656 

4.303 

.086 

4-50 

3/1  6 

•  1075 

3.766 

•  075 

3.7306 

.4102 

4-795 

.096 

4-75 

i/4 

.2272 

4-173 

.083 

3.9270 

.5625 

5-312 

.106 

5  -oo 

5/i  6 

•3530 

4.600 

.092 

4-1233 

.7227 

5.857 

.117 

5.25 

3/8 

.4849 

5-049 

.  101 

4.3197 

.8906 

6.428 

.128 

5-50 

7/1  6 

.6230 

5.518 

.  no 

4.5160 

.0664 

7  .026 

.141 

5-75 

1/2 

.7671 

6.008 

.  120 

4.7124 

.2500 

7.650 

•  153 

6.00 

From  formula  (i)  with  steel  ratio  .007. 


L  j? 
b  d2  = 


X  144  in.  span  X  23808 


=  5,791  cu.  ins. 


lib  =  12  ins.,  d2  = 


From  Table  XVII,  d  =  22  ins. 

With  2  inches  of  concrete  below  the  steel,  the  dimensions  will  be 
12  x  24  ins. 

From  Table  XVIII,  the  concrete  will  cost,  at  the  rate  of  $10.00 
per  cu.  yd. 

.741  X  12  =  $8.89 

From  formula  (2)  the  steel  area  will  be, 

.22  X  12  X  .007  =  1.85  sq.  ins. 


Handbook  for  Cement  and  Concrete  Users 

From  Table  XIX,  this  is  equal  to  the  area  of  5-5/8  inch  square 
bars,  and  from  the  same  table  the  cost  at  the  rate  of  2  cents  per 
pound  will  be 

5  X  12  X  .027  =  $1.62 

add  60  per  cent  for  the  cost  of  upper  flange  bars,  stirrups,  bent  ends, 
and  fabricating,  and  the  total  cost  will  be 

-Cost  of  steel 1.6  X  $1.62  =  $2.59 

Cost  of  concrete    8 . 89 


Total  cost $11 .48 

The  corresponding  costs  with  different  steel  ratios  will  be  found 
to  be  as  follows : 

.0055  lower  flange  steel  dimensions  12  X  25  ins.,  steel  5-9/16  in.  sq.  bars,  cost   $11.37 

.007        "         "  "  "  12  X  24   "       "      5-5/8     "     "     "         "       11.48 

.010  "  "  12   X    23      "          "         5-3/4       "       "       "  "          12.17 

.012  "  "  "  "  12    X    22      "          "         5-13/16"       "       "  "  12.47 

These  are  relative  costs  based  on  concrete  at  $10.00  per  cu.  yd., 
and  steel  at  2  cents  per  pound.  With  concrete  at  $15.00  per  cu. 
yd.,  the  beam  with  .007  steel  would  be  the  cheapest  in  cost. 

Design  of  Stirrups. — In  a  beam  supporting  a  uniformly  dis- 
tributed load,  stirrups  are  required  when  the  total  load,  including 
the  weight  of  the  beam  in  pounds,  divided  by  the  sectional  area  in 
square  inches,  exceeds  60,  or  when 

W  +  W 

—r-^ —  exceeds  60 (7) 

u  d 

Thus  in  the  previous  example,  W  +  W  =  23808,  6  =  12,  and  d  =• 
22,  and  since 

23808 

— =   00.2 

12    X   22 

stirrups  should  be  employed. 

Stirrups  are,  however,  desirable  in  all  beams,  as  they  add 
considerably  to  their  strength  and  ability  to  withstand  shocks. 
Stirrups  may  be  either  vertical  or  inclined.  They  are  most  efficient 
when  inclined  at  an  angle  of  45  degrees  toward  the  end  of  the  girder. 

Ransome's  Rule. — Mr.  E.  L.  Ransome's  rule  is  to  employ  four 
stirrups  at  each  end  of  the  beam,  the  first  at  1/4  of  the  depth  from 
the  end,  the  second  at  1/2  the  depth  from  the  first,  while  the  spacing 

[184] 


How  to  Design  Reinforced  Concrete 

of  the  third  is  3/4  of  the  depth  and  of  the  fourth,  a  distance  equal 
to  the  depth.  These  stirrups  are  in  general  composed  of  1/4  to 
3/8  inch  rods. 

Stirrups  should  go  through  the  beam  into  the  floor  slab,  where 
they  are  bent  to  run  parallel  with  the  slab  for  about  six  inches. 
Stirrups  should  always  be  fastened  to  or  looped  around  the  bottom 
rods.  In  place  of  stirrups  a  sheet  of  expanded  metal  or  other  wire 
fabric  may  be  placed  in  the  web  of  the  beam. 

An  improvement  over  the  use  of  loose  rods  and  stirrups  consists 
in  the  unit  system  of  reinforcement,  where  all  of  the  members  are 
assembled  into  one  frame.  These  are  illustrated  in  another  chapter, 
and  include  the  Kahn,  Cummings,  Unit,  and  Girder  frames. 

Design  of  Bond. — The  steel  bars  may  be  considered  safe  against 
slipping  when  not  called  upon  to  sustain  more  than  50  pounds  bond 
stress  per  square  inch  of  surface  area. 

In  a  beam  carrying  a  symmetrical  or  uniform  load,  this  con- 
dition may  be  expressed  by  the  following  formula: 

4  (W  +  W) 
-j— -  must  not  exceed  50     ....      (8) 

where  W  denotes  the  load  on  the  beam  in  pounds. 
W  denotes  the  weight  of  the  beam  itself. 
n  denotes  the  sum  of  the  perimeters  of  the  steel  bars  in  inches. 
d  denotes  the  depth  to  the  plane  of  the  steel  in  inches. 

In  the  previous  example,  W  4-  Wf  =  23,808,  d  =  22  ins.,  and  since 
5  —  5/8  inch  square  bars  are  used, 

4  X  5 

11  =  5  X  ~~8       =  I2'5  mches 
and 

4  X  23808 


-  =49.5  Ibs.  per  sq.  inch, 


7  X  12.5  X  22 

which  is  barely  within  the  required  limit  of  50.     With  a  greater 
bond  stress,  the  number  of  bars  would  need  to  be  increased. 

Summary  of  Method  of  Procedure  in  Design  of  Beams  and 
Slabs. — The  following  is  a  brief  summary  of  the  different  steps 
involved  in  the  design  of  a  beam  or  slab  carrying  a  uniformly  dis- 
tributed load,  as  previously  described  in  this  chapter. 

[185] 


Handbook  for  Cement  and  Concrete  Users 

(1)  Compute  the  total  load,  W,  on  the  beam. 

(2)  Estimate  the  weight,  W,  of  the  beam  itself. 

(3)  Compute  the  dimensions  of  the  beam  from  the  formula  : 


.   ....   .   .   . 

(4)  Compute  the  sectional  area,  A,  of  the  steel  from  the  formula  : 

A  ==  p  b  d    .......      (10) 

b  denotes  the  breadth  of  the  beam  in  inches. 
d  denotes  the  effective  depth  in  inches  to  the  plane  of  the  steel. 
/  denotes  the  length  of  the  span  in  inches. 
p  denotes  the  percentage  of  lower  flange  steel. 
D  denotes  the  denominator  of  formula  (9)    and  is  obtained  from 
Table  XVI  for  the  desired  value  of  p;  thus  for 
p  =  .007,  D  =  74;  for  p  =  .008,  D  =  78,  etc. 

(5)  Employ  from  7/10  to  i  per  cent  of  steel    in  the  lower  or 
tension  part  of  the  beam. 

(6)  If  girders  are  built  in  one  monolithic  length  over  three  or 
more  supports,  they  are  called  continuous  girders,  and  should  have 
at  least  four-tenths  per  cent  of  steel  in  the  upper  part  of  the  beam, 
extending  to  the  quarter-points.      In  continuous  slabs  the   steel 
should  be  in  the  lower  part  of  the  slab  at  the  centre  and  in  the  upper 
part  at  the  supports. 

(7)  In  large  beams,  employ  from  three  to  four  stirrups  or  pair 
of  stirrups  at  each  end,  composed  of  1/4  to  3/8  inch  rods,  and 
spaced  according  to  Ransome's  rule,  as  described  in  this  chapter. 

In  small  beams  use  steel  wire  or  metal  fabric.  Anchor  all  bars 
as  previously  explained,  and  securely  wire  all  loose  bars  in  such  a 
way  that  they  will  not  be  displaced  in  concreting,  and  so  that  the 
concrete  will  cover  all  bars  by  from  i  1/2  to  2  diameters  in  large 
beams  and  by  at  least  3/4  of  an  inch  in  thin  slabs.  Always  employ 

W  +  W 

stirrups  when  -  —  -  —  •  exceeds  60. 
b  d 

(8)  Test  the  bond  between  the  steel  and  concrete  by  the  formula  : 

4  (W  +  W) 

—7  -  must  not  exceed  so.        .      .      .      (n) 

7  nd  ,  . 

where  n  denotes  the  sum  of  the  perimeters  of  the  steel  bars  in  inches. 

[186] 


How  to  Design  Reinforced  Concrete 

Observe  the  following  general  rules. 

(9)  The  best-shaped  beam  is  one  in  which  the  breadth  is  from 
one-half  to  three-fourths  of  the  effective  depth. 

(10)  The  breadth  should  not  be  less  than  1/24  of  the  span, 
(n)  Stirrups  must  be  amply  provided  especially  when  the  depth 

is  greater  than  i/io  of  the  span. 

(12)  The  breadth  must  be  sufficient  for  the  spacing  of  the 
bars.     A  minimum  clear  spacing  of  at  least  11/2  diameters  should 
be  provided,  with  an  equal  distance  between  the  outside  rod  and  the 
surface  of  the  beam. 

(13)  Sufficient  rods  should  be  employed;   so  that  the  diameter 
of  each  will  not  exceed  i  /  200  of  the  span. 

(14)  The  length  of  rod  on  each  side  of  the  centre  of  the  beam 
should  be  at  least  80  diameters  for  plain  and  50  diameters  for  de- 
formed bars. 

(15)  Compare  the  computed  weight  with  the  estimated  weight 
of  the  beam,  and  revise  the  design  if  the  difference  exceeds  10  per 
cent. 

How  to  Design  a  Reinforced  Concrete  Column. — This  consists 
in  determining  proper  dimensions  for  the  post  or  column,  and  the 
steel  required  for  its  reinforcement.  The  following  order  of  com- 
putations should  be  observed. 

(1)  Compute  the  load,  P,  to  be  supported  by  the  column. 

(2)  Estimate  the  weight,  W,  of  the  column  itself. 

(3)  Determine  the  load  per  sq.  in.  of  sectional  area  which  the 
concrete  can  be  designed  to  carry,  also  the  ratio  between  the  moduli 
of  concrete  and  steel. 

(4)  Choose    the    percentage    of    vertical    reinforcement.     In 
general  this  should  be  between  i  and  2%  per  cent. 

(5)  If  spiral  wrappings  are  to  be  used,  choose  the  sectional  area, 
and  spacing  of  the  bands. 

(6)  Compute  the  sectional  area  required  for  the  column  by  the 
following  formula,  and  check  its  weight. 

P  +  W 

Ae  =  C  +  pC(r^         '       •       •       *       • 

As  =  pAe      .     .     .     .     .  "...   .     .     (13) 
[187] 


Handbook  for  Cement  and  Concrete  Users 

Ac=  the  sectional  area  of  the  column. 

As  =  the  sectional  area  of  the  vertical  reinforcement. 

Ae=  the  effective  area  of  the  column. 

Ah=  the  sectional  area  of  the  hooping. 

P  =  the  load  to  be  supported. 
W  =  the  estimated  weight  of  the  column  itself. 

C  =  the  safe  compressive  stress  for  concrete. 

p  =  the  percentage  of  vertical  steel  reinforcement. 

r  =  the  ratio  between  the  modulus  of  elasticity  of  steel  and  that 
of  concrete  in  compression. 

Where  bands  are  used,  the  section  of  the  column  contained 
within  the  spirals  may  be  designed  to  carry  50  per  cent  more  stress 
than  the  column  without  bands,  providing: 

(a)  The  wrapping  is  circular  in  form. 

(b)  A  thickness  of  two  inches  of  concrete  is  placed  outside  of 
the  bands,  for  protection,  but  not  considered  as  taking  any  part  of 
the  load. 

(c)  The  bands  are  of  sufficient  size  so  that  their  sectional  area, 
Ah,  divided  by  the  pitch,  s,  or  distance  between  spirals  is  not  less 
than  the  diameter  of  the  spiral,  D,  divided  by  500,  or 

— -  must  not  be  less  than —        .      .      .      .      (14) 
5  500 

The  following  practical  rules  should  also  be  observed: 

(7)  The  length  of  the  column  must  not  exceed  more  than  12 
times  its  least  lateral  dimension. 

(8)  The  vertical  steel  must  be  as  straight  as  possible,  and  rest 
upon  bed  plates  at  the  bottom.     When  the  bars  are  spliced,  the 
bars  must  not  be  lapped  and  wired,  but  the  end  of  the  upper  bar 
must  rest  on  the  top  of  the  lower  one,  and  be  held  in  place  by  sleeves 
made  of  pipe.     The  sleeves  should  be  24  diameters  long  and  the 
joints  should  also  be  stiffened  by  a  half-inch  bar  about  four  times  as 
long  as  the  sleeve,  which  is  set  alongside  of  but  not  in  contact  with 
the  reinforcement. 

(9)  In  all  large  columns  the  steel  should  be  protected  by  at  least  two 
inches  of  concrete,  and  in  small  columns  by  not  less  than  one  inch. 

(10)  The  percentage  of  steel  which  can  carry  the  entire  load 
when  stiffened  by  the  concrete  can  be  found  by  dividing  the  load 

[188] 


Handbook  for  Cement  and  Concrete  Users 

to  be  supported  in  pounds  by  16,000.  In  general  this  will  run  from 
4  to  6  per  cent. 

(n)  The  load  on  the  column  must  be  symmetrically  placed,  so 
that  the  centre  of  the  load  coincides  with  the  centre  of  the  column. 
If  the  load  bears  more  on  one  side  of  the  column  than  it  does  on  the 
other,  it  is  called  an  eccentric  load;  and  it  requires  a  larger  column 
to  carry  an  eccentric  than  it  does  to  carry  a  symmetrical  load.  An 
eccentrically  loaded  column  cannot  be  designed  by  the  methods 
explained  in  this  chapter. 

Example. — Design  a  square  reinforced  concrete  post,  10  feet 
long,  which  will  support  a  load  of  20  tons  without  spiral  wrappings. 

Solution. — (i)  P  =  20  X  2,000  =  40,000  Ibs. 

(2)  Estimate  W  at  1,500  Ibs. 

(3)  A  safe  load  for  concrete  in  compression  is  350  Ibs.  per  sq. 
in.,  and  a  safe  value  of  the  ratio,  r,  is  12. 

(4)  Employ  1.7  per  cent  of  vertical  reinforcement. 

.  N  40,000  +  1500  41500 

(5)  A= —  r  =  tL^__  =  I00  sq.  ms. 

350  +  .017  X  350  (12  -  i)        4I5-45 

or  10  x  10  ins. 

This  column  will  weigh  about 

10/12  X  10/12  X  10  X  144  =  1,000  Ibs.,  which  is  less  than  the 
assumed  weight  and  therefore  safe. 

The  area  of  the  steel  will  be : 

.017  X  10  X  10  =  1.70  sq.  ins. 

If  4  square  bars  are  used  the  area  of  each  will  be : 

1.70  -4-  4  =  .43  sq.  ins.  or  4-11/16  in.  square  bars  are  required. 

(6)  The  least  lateral  dimension  is  10  inches". 
10  inches  X  12  =  10  feet. 

As  the  length  of  the  post  is  10  feet  or  equal  to  the  above  value,  the 
design  is  permissible. 

Summarying  the  results  of  the  design,  we  have, 

External  load,  20  tons. 

Weight  of  column,  1,000  Ibs. 

Dimensions,  10  ins.  x  10  ins.  X  10  feet. 

Vertical  reinforcement,  4-11/16  inch  square  bars. 

Example  2. — Design  a  circular  reinforced  concrete  column  with 
spiral  wrappings  12  feet  long  which  will  support  a  load  of  59  tons. 


How  to  Design  Reinforced  Concrete 

Solution.—  (i)  P  =  59  x  2,000  =  118,000  Ibs. 

(2)  Estimate  Wr  at  4,000  Ibs. 

(3)  Take  C  at  350  and  r  at  12. 

(4)  Take  p  at  1.5  per  cent. 

(5)  For  hooping,  use  5/i6-inch  round  steel  or  oval  bars  having 
the  same  sectional  area  of  .076  sq.  ins.  and  let  the  spirals  be  spaced 
apart  or  have  a  pitch  of  2  inches. 

,,.  118000  +  4000  122000 


1.5  [(35Q 


or  diameter  of  spirals  =    A    2O°  =  16  ins. 

M  •  7854 

With  2  inches  of  concrete  outside  of  the  hooping,  the  diameter  of 
the  post  will  be  4  +  16  =  20  inches,  and  will  weigh 

.7854  X  20/12  X  20/12  X  12  X  144  =  3>77o  Ibs., 
which  is  less  than  the  estimated  weight  and  is  therefore  safe.     1.5. 
per  cent  of  steel   is  3  sq.  ins.,  which  is  equivalent  to  6  —  3/4  inch 
square  rods. 

From  (5)  Ah  =  .076  and  s  =  2  ins.,  also  from  (6),  D  =  16  ins., 

and  since  —  must  not  be  less  than  —  ,  '—-*—  must  not  be  less  than 
s  500     2 

16 
-  •;  or  since  .038  is  greater  than  .032  the  hooping  is  in  conformity 

with  the  condition. 

(7)  The  least  lateral  dimension  is  20  inches. 

20  inches  X  12  =  20  feet. 

As  this  is  greater  than  the  length  of  the  post,  the  design  easily  satisfies 
the  condition  as  to  the  ratio  of  length  to  least  lateral  dimension. 

Summarizing  the  results  of  the  design,  we  have  for  the  circular 
column 

External  load,  59  tons. 

Weight  of  column,  3,770  pounds. 

Diameter  of  column,  20  inches. 

Diameter  within  hooping,  16  inches. 

Length  of  column,  12  feet. 

Vertical  reinforcement,  6-3/4  inch  square  rods. 
Hooping,  5/16   inch  round  or  oval  bars  with  spirals  spaced  2 
inches  apart. 


How  to  Design  Reinforced  Concrete 


1  REINFORCEMENT  OF 
SLABS 

N| 

'ill 

</)  0 

HM                        He*                       He*                       HN 
O    O     i>-         \OOt-*         \O\Ot^         \O   vO     r^- 

vard,  one  rod  in  three,  or  two  rods  in  four  from  $  points  in  beam  to  top  of  beam  and  over  supports, 
shaped  with  bent  ends, 
s  placed  at  right  angles  to  supporting  beams.  Cross  reinforcement  of  slightly  smaller  rods  or  same  rods  farther  apart 
labs  parallel  to  beams, 
ded  metal  mesh  may  be  substituted  for  rods  in  the  slabs,  provided  the  area  of  section  of  metal  is  kept  the  same  as  the  rods, 
.d  not  be  used  for  beams.  6.  Cinder  concrete  may  be  used  for  roof  slabs  if  thickness  is  increased  one  inch. 
s,  test  two  of  the  slabs  and  one  beam  by  loading  two  panels  with  sand  to  depth  of:  18  inches  deep  for  heavy  floor  loading; 
ght  floor  loading;  5  inches  deep  for  roof  loading, 
ctory  Construction,"  published  by  the  Atlas  Portland  Cement  Co.  *  Place  first  stirrup  in  every  case  6  inches  from  support. 

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Handbook  for  Cement  and  Concrete  Users 


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[192] 


How  to  Design  Reinforced  Concrete 


REINFORCEMENT  OF 
SLABS 

S'SS 

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VO      W>    «>•            VO      IO    t~»            \O      IO    !>.            \O      »O    t*» 

hree,  or  two  rods  in  four  from  i  points  in  beam  to  top  of  beam  and  over  supports, 
nds. 
angles  to  supporting  beams.  Cross  reinforcement  of  slightly  smaller  rods  or  same  rods  farther  apart 
ims. 
ay  be  substituted  for  rods  in  the  slabs,  provided  the  area  of  section  of  metal  is  kept  the  same  as  the  rods 
earns.  6.  Cinder  concrete  may  be  used  for  roof  slabs  if  thickness  is  increased  one  inch, 
labs  and  one  beam  by  loading  two  panels  with  sand  to  depth  of  :  18  inches  deep  for  heavy  floor  loading; 
inches  deep  for  roof  loading. 

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193! 


CHAPTER  XVIII 


EXPLANATION  OF  THE  THEORY  OF  THE  DESIGN  OF 
REINFORCED  CONCRETE  BEAMS  AND  SLABS 

Explanation  of  the  Theory  of  the  Design  of  Reinforced  Concrete  Beams  and  Slabs,  and 
General  Specifications  for  Reinforced  Concrete. — The  Mechanics  of  the  Beam, 
Stresses,  and  Moments. — Derivation  of  Formulas. 

IN  the  previous  chapter  the  method  of  designing  a  simple  beam  carrying  a  uniformly 
distributed  load  was  presented,  and  a  number  of  formulas  were  employed.  In  this 
chapter  the  distribution  of  stress  in  a  beam  is  explained,  and  other  formulas  are  de- 
veloped which  are  applicable  to  beams  carrying  concentrated  as  well  as  distributed 
loads,  and  to  cantilever  as  well  as  simple  beams.  This  chapter,  while  largely  theoreti- 
cal, will  serve,  perhaps,  as  an  introduction  to  a  more  extensive  study  of  the  mechanics 
of  materials  which  can  then  be  profitably  pursued.  The  best  book  for  the  student  on 
reinforced  concrete  design  is  Turneaure  and  Maurer's  "Principles  of  Reinforced 
Concrete  Construction,"  but  a  study  of  this  work  should  be  preceded  by  a  course  in 


O 


T 


FIG.  50. 


FIG.  51. 


Applied  Mechanics,  such  as  is  contained  in  Church's  "Mechanics  of  Engineering, '» 
Merriman's  "Mechanics  of  Materials,"  or  other  standard  text  books  on  the  subject. 
This  chapter  is  printed  in  smaller  type  so  that  it  may  be  omitted  by  the  reader  who 
does  not  wish  to  go  into  the  theory  of  reinforced  concrete. 

DESIGN  OF  BEAMS. — Before  taking  up  the  study  of  reinforced  concrete  beams,  it 
is  necessary  to  consider  what  takes  place  in  a  simple  wooden  beam  of  rectangular 
section  when  acted  upon  by  external  forces.  Such  a  beam  is  shown  in  Fig.  50,  resting 
on  two  supports  an'1  carrying  a  weight  at  the  centre. 

By  replacing  the  supports  and  centre  load  by  arrows  representing  by  their  lengths 
the  forces  acting  on  the  beam,  we  have  Fig.  51,  in  which  the  centre  load  is  shown 
pressing  downward  while  the  beam  is  held  in  equilibrium  by  the  upward  pressures  at 
the  points  of  support. 

If  the  load  is  exactly  in  the  centre,  it  is  evident  that  half  of  this  load  will  be  carried 
to  each  support,  so  that  the  reactions  or  upward  pressures  of  the  supports  against  the 
beam  will  be  equal. 

[194] 


Explanation  of  the  Theory 


If,  however,  the  load  is  nearer  one  end  of  the  beam  than  the  other,  it  is  evident  that 
the  support  which  is  nearest  to  the  load  will  carry  more  than  half  of  the  weight  while 
the  further  support  will  carry  less  than  half. 


THE    MECHANICS    OF    THE    BEAM.      LOADS,    REACTIONS, 
AND    MOMENTS 

The  different  kinds  of  stresses  developed  in  beams,  subjected  to  loading,  have  been 
described  at  the  beginning  of  the  previous  chapter.  We  will  now  consider  how  the 
loads  are  carried  and  distributed  to  the  supports  and  their  effect  in  producing  bending. 

When  a  horizontal  beam  carries  a  single  load,  the  reaction  or  upward  pressure  on 
the  beam  at  either  support  due  to  the  load  is  found  by  multiplying  the  load  by  the  dis- 


! 


6 


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-  J    - 


FIG.  52. 


FIG..  53. 


tance  from  the  line  of  action  of  the  load  to  the  line  of  action  of  the  other  support,  and 
dividing  by  the  distance  between  supports. 

Thus  in  Fig.  5  2,  the  reaction  at  the  right  support,  R2  is  equal  to  — — =  750  Ibs. 

and  at  the  left  support  ^  =  — — =  250  Ibs.,  neglecting  the  weight  of  the  beam 

itself;  and  the  sum  of  the  reactions,  R2  +  ^  =  750  +  250  =  1,000  Ibs.,  the  total 
load  on  the  beam. 

If  the  beam  carries  more  than  one  load,  the  reaction  due  to  the  loads  at  either 
support  is  found  in  a  similar  way  by  adding  the  products  obtained  by  multiplying  each 
load  by  its  moment  arm  or  distance  from  the  line  of  action  of  the  load  to  the  line  of 
action  of  the  other  support,  and  dividing  by  the  distance  between  supports. 

If  the  beam  also  carries  a  uniformly  distributed  load,  as  the  weight  of  the  beam  itself, 
half  of  this  load  will  also  be  carried  by  each  support. 


r™          •      T-  T,          «n««v      •      3.000   X    I       ,      2,000   X  5       ,       1,000  X 

Thus  in  Fig.  53,  *i  =  V   +         I0         +         I0         +  — ~ 


R}  =  2,000  +  300  +  1,000  4-  800  =  4,100  Ibs. 


and 

while 


Si90olbt, 


j  -f- 


2  10  10  10 

4,100  +  5,900  =  10,000  Ibs.,  the  total  load  on  the  beam. 

[195] 


Handbook  for  Cement  and  Concrete  Users 


Bending  Moments  and  Internal  Stresses. — The  loads  on  a  beam  do  more  than  exert 
pressure  on  the  points  of  support.  They  also  produce  internal  stresses  in  the  beam 
itself,  as  is  shown  by  the  bending  of  a  plank  when  carrying  a  load  across  a  span. 

The  stresses  produced  in  a  simple  horizontal  beam  carrying  a  load  are  compression 
in  the  upper  portion,  tension  in  the  lower  portion,  and  shear.  Compression  is  greatest 
at  the  upper  surface  and  decreases  to  zero  at  the  neutral  plane;  tension  is  greatest  at 
the  lower  surface  and  also  decreases  to  zero  at  the  neutral  plane.  In  a  wooden  beam 
of  rectangular  section  lying  in  a  horizontal  position,  the  neutral  plane  or  plane  in  which 
the  material  is  neither  compressed  nor  stretched,  is  midway  between  the  upper  and 
lower  surfaces. 

In  Fig.  54,  ahck  represents  half  of  a  rectangular  beam  cut  in  two  at  the  point 
of  application  of  the  load,  Pv  b  is  the  breadth  and  d  the  depth  of  the  beam,  Rl  is  the 
reaction  or  upward  pressure  on  the  beam  at  the  left  support,  and  the  arrows  represent 

%  /?  P. 


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FIG.  54. 

by  their  lengths  the  variation  of  compressive  stress  from  the  upper  to  the  neutral 
surface  and  of  tensile  stress  from  the  lower  to  the  neutral  surface.  The  neutral  axis  is 
the  intersection  of  the  neutral  surface  with  any  plane.  In  Fig.  54,  the  line  /  g  is  the 
neutral  axis,  while  the  lines  n  o  and  p  t  are  called  extreme  fibres;  e  is  the  distance  from 
the  neutral  axis  to  the  extreme  fibre  in  compression,  and  e'the  distance  from  the  neutral 
axis  to  the  extreme  fibre  in  tension.  In  a  wooden  beam  of  rectangular  section,  e'  is 
equal  to  e.  In  a  reinforced  concrete  beam  e'  is  greater  than  e. 

The  internal  stresses  represented  by  the  arrows  hold  in  equilibrium  the  external 
forces  on  either  side  of  the  section  where  the  beam  is  cut  in  two.  These  external 
forces  Rv  Pv  P2  and  Py  tend  to  produce  rotation  of  the  beam,  while  the  internal 
stresses  represented  by  the  arrows,  resist  the  tendency  of  the  beam  to  rotate. 

For  example,  in  Fig.  54,  the  upward  pressure  of  the  reaction  ^  tends  to  produce 
clockwise  rotation,  of  the  beam  about  the  point  g,  and  this  is  resisted  in  part  by  the 
downward  pressures  Pv  P2,  and  P3,  and  in  part  by  the  internal  stresses  represented 
by  the  arrows. 

[196] 


Explanation  of  the  Theory 


The  effect  of  a  force  in  tending  to  produce  rotation  is  the  product  of  the  force  by 
the  distance  between  its  line  of  application  and  the  centre  of  movement.  Thus  the 
effects  of  the  forces  Rv  P2,  and  P3,  in  producing  rotation  about  the  point  g,  are  Rl  /, 
P2  /2,  and  P3  13,  and  their  combined  effect  is  expressed  by  Rt  l—P2  12  —  P3  13.  Each 
of  these  products  is  called  a  moment,  and  the  algebraic  sum  of  the  moments  due  to 


i  11    \ 

\    :       : 

1  -! 

^Zf^-3t 

t                               ,       ' 
1                                     it 

t                               1 

FIG.  55. 

the  loads  and  the  reaction  between  the  point  of  support  and  any  section  of  a  beam  is 
called  the  bending  moment  at  that  section. 

For  example,  it  is  required  to  find  the  bending  moment  at  each  loaded  section  of 
the  beam  represented  in  Fig.  55. 

The  reactions  R^  and  7x2  must  first  be  computed. 

(3,000  X  12)  +  (2,000  X  60)  +  (1,000  X  96) 

A     =  =   2,IOO  IDS. 

120 

(1,000  X  24)  -f  ( 2,000  X  60)  4-  (3,000  X  108) 
R2  =  -  I20  -  3,900  Ibs. 

The  bending  moment  under  the  2,ooo-lb.  load  is  therefore  (2,100  X  60)  —  (1,000 
X  36)  =  90,000  inch-pounds. 

Under  the  i,ooo-lb.  load,  the  bending  moment  is  (2,100  X  24)  =  50,400  inch- 
pounds. 

Under  the  3,ooo-lb.  load,  the  bending  moment  is  (3,900  X  12)  =  46,800  inch- 
pounds. 

Hence  the  position  of  maximum  bending  moment  is  under  the  2,ooo-lb.  load. 

In  a  beam  supported  at  each  end  and  carrying  a  uniformly  distributed  load  of  W 
pounds,  the  maximum  bending  moment  is  at  the  centre  of  the  span,  and  if  the  length 
of  the  span  be  represented  by  /, 

Max.  mom.  =  1/8  W I  .      .     .     .     .     .-  .      .     (i) 

If  the  weight  of  the  beam  itself  be  taken  into  account  and  represented  by  W, 

Max.  mom.  =  1/8  /  (W  +  W) .     .   •.     ....      .     (i') 

In  a  similar  beam,  carrying  a  single  concentrated  load  P  at  the  centre  of  the  span, 
the  maximum  moment  due  to  the  load  is  also  at  the  centre  of  the  span,  and  its  value  is 

Max.  mom.  =  1/4  PI     .     .     .     .     .     .     .     .     (2) 


Handbook  for  Cement  and  Concrete  Users 

If  the  weight  of  the  beam  is  taken  into  account, 

Max.  mom.  1/4  P I  +  1/8  W  I (2') 

A  cantilever  beam  is  supported  at  one  end  only,  which  is  fixed  or  built  into  a  wall. 
In  such  a  beam  the  maximum  moment  is  over  the  point  of  support.  When  carrying 
a  uniformly  distributed  load  W  over  a  span  having  a  length  /,  the  maximum  moment  is 

Max.  mom.  =  1/2  W I (3) 

When  carrying  a  single  concentrated  load  P  at  the  end  of  the  cantilever  arm,  the 
maximum  moment  is 

Max.  mom.  =  P I          .      . (4) 

When  both  ends  of  the  beam  are  restrained  or  built  into  a  wall,  the  maximum  bending 
moment,  under  a  uniformly  distributed  load  W  is  at  the  wall,  and  its  numerical  value  is 

Max.  mom.  =  1/12  W I          (5) 

When  a  beam  is  built  continuously  over  three  or  more  supports  it  is  called  a  continuous 
girder,  and  the  distance  between  each  pair  of  supports  is  the  span. 

In  a  continuous  girder  with  two  equal  spans,  carrying  a  uniformly  distributed  load 
Wy  with  supports  on  the  same  level,  the  maximum  moment  occurs  over  the  middle 
support,  and  its  numerical  value  is 

Max.  mom.  =  1/8  W I (6) 

In  a  continuous  girder  with  three  equal  spans,  carrying  a  uniformly  distributed  load 
W  with  supports  on  the  same  level,  the  maximum  moment  occurs  over  the  two  middle 
supports  and  its  numerical  value  is 

Max.  mom.  =  i/io  W I (6') 

In  cantilever,  restrained,  and  continuous  beams,  where  moments  occur  over  a 
support,  such  moments  are  called  negative  bending  moments. 

Where  a  negative  bending  moment  occurs  in  a  horizontal  beam,  the  internal  stresses 
produced  by  the  negative  bending  moment  are  the  reverse  of  those  which  take  place 
in  a  simple  beam.  Where  a  negative  mornent  occurs,  the  upper  part  of  the  beam  is  in 
tension  and  the  lower  part  in  compression.  Tension  is  greatest  in  the  upper  and 
compression  in  the  lower  surface,  and  between  the  upper  and  lower  surfaces  is  the 
neutral  surface  where  the  moment  stress  is  zero. 

In  a  cantilever  beam,  the  negative  bending  moment  occurs  the  whole  length  of  the 
span  and  is  greatest  at  the  support .  Hence  a  reinforced  concrete  beam,  when  designed 
to  act  as  a  cantilever,  should  have  the  main  horizontal  bars  near  the  top  of  the  beam, 
while  the  lower  half  must  have  sufficient  concrete  to  take  care  of  the  compression.  As 
the  greatest  stresses  occur  at  the  point  of  support,  particular  care  must  be  taken  to 
provide  sufficient  steel  and  concrete  at  this  point. 

In  restrained  and  continuous  girders  positive  moments  occur  in  the  centre  of  the 
span,  while  negative  moments  occur  over  the  supports.  Hence  such  beams  should 
have  horizontal  steel  bars  at  both  top  and  bottom.  Over  the  supports  horizontal  bars 
are  required  at  the  top  of  the  beam,  while  in  the  centre  of  the  span  the  reinforcement 
is  needed  at  the  bottom. 

The  length  of  span  over  which  a  negative  moment  is  likely  to  occur  depends  upon 
the  loading.  Under  extreme  conditions  this  may  occur  entirely  across  the  span.  In 


Explanation  of  the  Theory 


general  the  top  reinforcement  should  extend  from  1/4  to  1/3  of  the  span  on  each  side 
of  the  point  of  support. 

Having  found  the  amount  and  position  of  the  maximum  bending  moment  in  inch- 
pounds  at  any  section  of  a  simple  rectangular  beam  supported  at  each  end,  the  corre* 
spending  internal  stresses  in  the  beam  may  now  be  computed. 

In  Fig.  56,  let  ah  c  k  represent  part  of  a  horizontal  beam  with  two  end  supports, 
cut  in  two  along  the  line  c  k  and  loaded  in  any  way  with  loads  Pv  P2,  P3,  etc. 

Let  6"  =  the  greatest  internal  stress  in  the  beam.      Since  the  internal  stress  in  a 

rectangular  beam  decreases  uniformly  from  the  extreme  fibre  to  the  neutral  axis,  the 

^ 
average  stress  in  the  section  will  be — .     This  will  be  a  compressive  stress  in  the  upper, 

and  a  tensile  stress  in  the  lower  half  of  the   beam. 

Since  the  centre  of  gravity  of  a  triangle  is  1/3  of  the  distance  from  the  base  to  the 
apex,  the  point  of  application  of  the  resultant  of  the  cpmpressive  stresses  in  a  rec- 


f? 


FIG.  56. 


tangular  beam,  of  homogeneous  material,  is  1/3  of  the  distance  from  the  upper  surface 
to  the  neutral  axis,  or  (since  e  is  equal  to  e'),to  1/6  of  the  depth  of  the  beam,  and  sim- 
ilarly the  resultant  of  the  tensile  stresses  is  1/6  of  the  depth  of  the  beam  above  the  lower 
surface. 

If  b  is  the  breadth  and  d  the  depth  of  the  beam,  the  surface  under  compression  is 
1/2  d  b,  which  is  also  the  area  of  the  surface  under  tension.  The  moment  area  of  the 
resultant  of  the  compressive  stresses  about  the  neutral  axis  will  be  2/6  d,  and  similarly 
of  the  tensile  stresses  2/6  d,  while  the  resisting  moment  of  the  beam  will  be 


-J  (1/2  d  b  X  2/6  d)  +  (1/2  d  b  X  2/6  d~) 


1/6  Sbd2 

Hence  for  a  horizontal  rectangular  beam  o}  homogeneous  material  supported  at  each 
end  and  loaded  in  any  manner, 

M  =  1/6  S  b  d2 (7) 


•  Handbook  for  Cement  and  Concrete  Users 

This  equation  enables  the  dimensions  of  a  wooden  beam  to  be  computed,  which 
will  sustain  a  given  bending  moment,  M,  without  producing  an  internal  stress  greater 
than  S,  which  can  be  given  any  safe  value.  It  also  applies  to  a  plain  concrete  beam, 
but  not  to  a  reinforced  concrete  beam,  since  a  reinforced  beam  is  not  homogeneous. 

EXAMPLE. — It  is  required  to  find  suitable  dimensions  for  a  wooden  rectangular 
beam,  carrying  a  concentrated  load  of  2,000  pounds  at  the  centre  of  a  120-inch  span, 
without  producing  an  internal  stress,  S,  in  the  timber  greater  than  1,000  Ibs.  per  sq. 
in.,  neglecting  the  weight  of  the  beam  itself. 

Solution. — From  equation  (2),  M  =  1/4  P  I  and  from  (7)  M  =  1/6  5  b  d?,  hence 
equating:  1/4  P  /  =  1/6  .S  &  <*2  or 

1/4  X  2,000  X  120  =  1/6  X  1,000  b  d2 
b  d2  =  360  sq.  ins. 

since  /  is  in  inches  and  6"  is  in  pounds  per  sq.  in. 

If  b  =  4  inches,  d?=  - —  =  90,  and  d  =  9.5  ins. 
4 

Hence  a  beam  10  ins.  deep  by  4  ins.  wide  will  carry  the  load  with  a  maximum  in- 
ternal stress  of  1,000  Ibs.  per  sq.  in.  in  the  extreme  fibre,  neglecting  the  weight  of  the 
beam  itself. 

Shear  at  any  Section  of  a  Beam. — The  loads  on  a  beam  are  not  directly  over  the 
supports,  and  this  results  in  what  are  called  shearing  stresses.  At  either  support,  the 
vertical  shear  is  equal  to  the  upward  push  of  the  support  against  the  beam,  and  at 
any  section  of  the  beam  it  is  equal  to  the  upward  push  of  the  support  at  either  end 
diminished  by  the  sum  of  the  intervening  loads.  Hence  the  greatest  shear  is  at  the 
support  which  carries  the  heaviest  end  of  the  beam,  and  in  reinforced  concrete  beams 
a  portion  of  the  steel  is  bent  up  at  intervals  near  the  supports  in  order  to  take  care  of 
this  shear.  When  a  beam  carries  a  uniform  or  symmetrical  load,  the  greatest  shear 
is  equal  to  half  of  the  load. 

Derivation  of  Straight  Line  Formulas  for  Reinforced  Concrete  Beams. — Reinforced 
concrete  is  most  economically  employed  in  beams,  when  the  steel  is  designed  to  carry 
the  entire  tensile  stress,  as  by  so  doing  the  strength  of  the  steel  may  be  fully  brought 
into  play.  When  the  concrete  is  designed  to  carry  a  portion  of  this  stress,  the  full 
strength  of  the  steel  is  not  developed,  as  is  shown  by  the  following  considerations: 

The  modulus  of  elasticity  or  the  ratio  between  the  length  of  a  rod  and  its  elongation 
under  a  tensile  force  of  one  pound  per  square  inch  is  about  30,000,000  for  steel  and 
from  2,000,000  to  3,000,000  for  concrete,  so  that  the  ratio  of  E8  to  Ec  lies  between 
15  to  i  and  10  to  i.  In  practice  various  values  of  this  ratio  are  used,  depending  upon 
the  kind  of  concrete  and  the  judgment  of  the  designer.  In  this  volume,  a  value  of 
12  to  i  is  employed,  as  this  is  the  ratio  most  frequently  specified  in  building- codes  or 

Es  :EC  :  :  12  :  i 

According  to  Hooke's  law,  stress  is  proportional  to  strain.  Hence,  so  long  as  the 
adhesion  between  steel  and  concrete  is  unimpaired,  their  stresses  will  be  proportional 
to  their  moduli  of  elasticity  or  in  the  ratio  of  12  to  i. 

Again  the  safe  working  tensile  stress  of  concrete  is  about  50  pounds  per  sq.  in., 
and  if  the  concrete  takes  its  share  of  tension,  the  corresponding  stress  in  the  steel  will 
be  only  12  x  50  =  600  Ibs.  per  sq.  in. 

Since  steel  can  safely  be  designed  to  carry  from  15,000  to  20,000  Ibs.  per  sq.  in.  in 
tension,  it  is  evident  that  in  reinforced  tension  members,  we  must  either  use  very  low 

[200] 


Explanation  of  the  Theory 


and  uneconomical  working  stresses  for  steel,  or  else  expect  the  concrete  to  be  of  no  as- 
sistance in  carrying  stress. 

In  this  discussion,  the  formulas,  which  are  developed,  are  based  on  the  assumption 
that  the  steel  carries  the  entire  tensional  stress. 

In  a  reinforced  concrete  beam  the  compressive  stress  is  greatest  in  the  outer  fibre 
and  decreases  to  zero  at  the  neutral  axis.  Experiments  indicate  that  the  stress-strain 
curve  approximates  most  closely  to  a  parabola,  but  many  designers  for  the  sake  of 
simplicity  consider  the  stress  to  vary  uniformly  or  as  the  ordinates  to  a  straight  line. 

In  this  discussion  the  compressive  stress  on  a  vertical  section  is  considered  to  vary 
in  intensity  in  direct  proportion  to  its  distance  from  the  neutral  axis,  or  as  the  ordinates 
to  a  straight  line,  which  assumption  errs,  if  at  all,  on  the  side  of  safety,  as  it  results  in 
more  concrete  being  employed  than  is  the  case  when  the  parabolic  theory  is  adopted. 

The  following  notation  is  employed: 

S  denotes  the  unit  fibre  stress  in  the  steel. 
C  denotes  the  unit  fibre  stress  in  the  concrete  in  compression, 
e/denotes  the  unit  elongation  of  the  steel  due  to  S. 
ec  denotes  the  unit  shortening -of  the  concrete  due  to  C. 
Eg  denotes  the  modulus  of  elasticity  of  the  steel. 
Ec  denotes  the  modulus  of  elasticity  of  the  concrete  in  compression. 

Tf 

r  denotes  the  ratio  — =-  • 
J^c 

T  denotes  the  total  tension  in  the  steel  at  a  section  of  the  beam. 

P  denotes  the  total  compression  in  the  concrete  at  a  section  of  the  beam. 

M8  denotes  the  resisting  moment  as  determined  by  the  steel. 

Mc  denotes  the  resisting  moment  as  determined  by  the  concrete. 

M  denotes  the  bending  or  resisting  moment  in  general. 

b  denotes  the  breadth  of  a  rectangular  beam. 

d  denotes  the  distance  from  the  compression  face  to  the  plane  of  the  steel. 

k  denotes  the  ratio  of  the  depth  of  the  neutral  axis  of  a  section  below  the  top  to  d. 

k  d  denotes  the  depth  of  neutral  axis  below  top  of  beam. 

j  denotes  the  ratio  of  the  arm  of  the  resisting  couple  to  d. 

j  d  denotes  the  arm  of  the  resisting  couple. 

A  denotes  the  area  of  cross-section  of  steel. 

A 
p  denotes  the  steel  ratio  -7-7-. 

When  a  beam  bends  under  its  load,  it  is  assumed  that  any  section,  such  as  would 
be  made  by  a  vertical  saw  cut  remains  plane  after  bending. 

It  therefore  follows  that  the  unit  deformations  of  the  fibres  vary  as  their  distances 
from  the  neutral  axis,  or 

es_    __  d  -  kd 
ec    ''         kd 

S  C 

also  es  =  —    and  ec  =  — 

ES  EC 

S 

Es     _  d-  kd      S  EC  _  d-  kd 
"(T  kd      °TC~Es~~~kd~ 

EC 

E8  S         d-  kd        i-  k 

and  since  r  =  -77-  we  have  —•=  =  — .    ,  ••    =  — r — (a) 

EC  rC  K  a  K 


201] 


Handbook  for  Cement  and  Concrete  Users 


In  a  horizontal  beam,  Fig.  57,  with  vertical  loads  and  reactions,  the  total  tension 
and  compression  on  any  section  are  equal,  and  since  the  average  compressive  stress 
is  equal  to  one-half  of  the  maximum  stress,  C,  in  the  outer  fibre, 

SA   (the  total  tension)  =  1/2  C  b  k  d  (the  total  compression)        .      .     (b) 
Eliminating  —  between  equation  (a)  and  (b)  and  introducing   the    abbreviation 
P  =    -j—j  we  have,  2  pr  (i  —  k)  =  k2,  which,  if  solved  for  K,  gives 

k  =  \/2  p  r  +  (p  r)2  -  pr        .......     (8) 

The  above  formula  (8)  shows  that  the  neutral  axes  of  all  beams  of  a  given  concrete 


H- 
I 


FIG.  57. 


-_   £    _- 


and  of  a  given  percentage  of  steel  are  at  the  same  proportionate  depth,  k,  for  all  work- 
ing loads. 

Since  the  centre  of  gravity  of  a  triangle  is  one-third  the  distance  from  its  base,  the 
distance  of  the  resultant  of  the  compressive  stress  from  the  compressive  face  of  the 
beam  is  1/3  k  d;  therefore  the  arm  of  the  resisting  couple,  T  P,  is  given  by 


j  d  =  d  -  1/3  k  d  or  ;  =  i  -  1/3  k 


(9) 


The  resisting  moment  is  equal  to  the  total  tension,  J1,  or  compression,  P,  multiplied 
by  its  moment  arm,  ;  d. 

If  the  beam  is  under-reinforced,  its  resisting  moment  depends  on  the  steel,  and  its 
value  then  is: 

Ms=Tjd=SAjd=Spbdjd=Spjbd2      .      .      .      .     (c) 

If  over-reinforced,  the  resisting  moment  depends  on  the  concrete,  and  its  value  then  is 
Mc  =  P  jd  =  1/2  C  b  k  d  j  d  =  1/2  C  k  j  b  d2       .      .      .      .     (</) 

The  resisting  moment  of  the  beam  must  be  equal  to  or  exceed  the  bending  moment 
due  to  the  external  loads,  hence: 


M  =  Mc  =  1/2   Ckjbd2  or  C  = 


and 


£76 


(10) 


M  =  Ms  =  S  p  j  b  d*  or  5 
[202] 


M 


pjbd2 


Explanation  of  the  Theory 

Formulas  (10)  and  (n)  are  used  to  find  the  unit  stresses  C  and  5  in  a  rectangular 
beam  after  it  has  been  designed.  They  are  called  check  formulas  because  frequently 
employed  to  test  a  beam  as  to  its  compliance  with  the  specifications. 

Also  since  M  =  S  pjbd2  and  M  also  =  1/2  C  k  j  b  d2,  therefore 


Spjbd2=i/2Ckjbd2 

C  1? 
and  5  = 


while  bd2  =  •      •      '      .......     (I3) 


Formula  (13)  is  used  for  finding  the  breadth,  b,  and  effective  depth,  d,  of  a  rectangular 
beam,  for  limiting  values  of  C,  S,  and  r. 

Steps  in  the  Procedure  for  the  Design.  —  Formulas  (7-12)  are  readily  adapted  for 
use  by  proceeding  in  the  following  manner: 

(1)  Assume  values  of  C  and  r,  as  for  example,  C  =  500,  and  r  =  12,  which  are  the 
maximum  values  permitted  in  the  building-code  of  New  York  City. 

(2)  Assume  different  values  of  /»,  as,  for  instance,  p}  =  .005,  p2  =  .006,  p3  =  .007, 
etc.,  and  solve  for  the  corresponding  values  of  k,  j,  and  S. 

k  is  computed  from  formula  (8);  ;'  from  (9),  and  S  from  (12). 

(3)  Multiply  together  the  corresponding  values  of  S  p  and  j. 

(4)  Tabulate  the  values  of  k,  5,  ;,  and  the  product  S  p  j  for  each  assumed  value 
of  p. 

(5)  If  other  values  of  C  or  r,  or  both  are  required,  prepare  another  table,  based  on 
such  values. 

For  example,  if  C  —  500  and  r  =  12,  for  p  =  .007,  substituting  values  of  p  and  r  in 
equation  (8),  we  have 


k  =\/(2  X  .007  X  12)  +  (.007  X  i2)2  -  (.007  X  12)  =  .334 
7=1  —  1/3  k  =  (i  —  .111)  =  .889  from  (9), 
C  k         <;oo  X  .  T,T,4 


and  the  product  S  pj  =  11929  X  .007  X  .889  =  74.2. 

Values  of  k,  j,  S,  and  the  product  S  p  j  are  tabulated  for  values  of  p,  ranging  from 
.005  to  .020  in  the  following  table.  This  table  will  be  found  convenient  for  use  with 
check  formulas  (10)  and  (n)  and  beam  formula  (13). 

p  =  percentage  of  steel  reinforcement;  b  =  breadth  and  d  =  depth  of  beam  in 
inches;  j  d  =  distance  from  the  point  of  application  of  the  resultant  of  the  compressive 
stresses  to  the  plane  of  the  steel,  and  k  d  the  distance  of  the  neutral  axis  from  the  extreme 
fibre  in  compression;  M  the  maximum  bending  moment  induced  by  the  external  loads 
in  inch-pounds;  S  and  C  the  respective  unit  fibre  stresses  in  the  steel  and  concrete  in 
pounds  per  sq.  inch;  and  r  the  ratio  of  the  modulus  of  elasticity  of  steel  to  that  of  con- 
crete; /  =  the  span  in  inches,  W  a  uniformly  distributed  load  on  the  beam,  and  W  the 
weight  of  the  beam  itself. 

The  first  and  fifth  columns  of  Table  XVlA  are  identical  with  Table  XVI  of  the  pre- 
ceding chapter,  neglecting  fractions,  which  for  simplicity  were  omitted  in  that  chapter 
as  they  do  not  materially  affect  the  design. 

[203] 


Handbook  for  Cement  and  Concrete  Users 


TABLE   FOR   USE   IN   DESIGNING   REINFORCED   CONCRETE  BEAMS 


based  on 


OF   RECTANGULAR   SECTION 


C  =  500  Ibs.  per'sq.  in.,  r  =  12,  b  d?  = 

TABLE    XVlA. 


M 
Spj' 


p 

k 

i 

5 

spj 

.005 

.291 

•9°3 

14550 

65-7 

.006 

.314 

.895 

13083 

70-3 

.007 

•334 

.889 

11929 

74.2 

.008 

•353 

.882 

11030 

77.8 

.009 

•369 

.877 

10250 

80.9 

.010 

.384 

.872 

9600 

83-7 

.on 

•399 

.867 

9068 

86.5 

.012 

.412 

.863 

8583 

88.9 

.013 

.424 

•859 

8154 

91.1 

.014 

-436 

•855 

7786 

93-2 

.015 

.446 

•851 

7433 

94-9 

.O2O 

•493 

.836 

6163 

103.0 

In  the  preceding  chapter,  the  following  formula  was  presented  for  determining  the 
dimensions  of  beams  carrying  a  uniformly  distributed  load: 


This  formula  was  obtained  in  the  following  way: 
From  (i')  max.  mom.  =  M  =  1/8  /  (W  +  W) 
M 


From  (13)  bd? 


Spf 


Substituting  1/8  /  (W  +  W'}  for  M,  we  have 


From  Table  XVI  A,  neglecting  fractions,  S  p  j  =  74  for  p  =  .007. 
Hence,  substituting  74  for  Spj  gives 

,  J2       i/Sl(W+Wr)  f 
b  d2  =  —  -  -  —        -  for  p  =  .007. 
74 

In  a  similar  way,  by  combining  formulas  2,  3,  4,  5,  and  6,  with  formula  13,  we 
obtain  the  following: 

For  simple  beams  carrying  a  single  concentrated  load,  P,  at  the  centre  of  the  span, 
and  weighing  W  pounds,  the  span  being  /  inches  long: 


1/8  W  I  4-  1/4  PI 

Spj 
[204] 


(15) 


Explanation  of  the  Theory 


For  simple  beams  carrying  both  a  uniformly  distributed  load,  W,  and  a  concentrated 
load,  P,  at  the  centre  of  the  span, 


Spj 
For  cantilever  beams  carrying  a  uniformly  distributed  load  W, 


For  cantilever  beams  carrying  a  single  concentrated  load,  P,  at   the  end  of  the 
cantilever  arm, 


For  cantilever   beams  carrying  both  a  uniformly  distributed  load,  W,  and  a  con- 
centrated load,  P,  at  the  end  of  the  cantilever  arm, 


.      ,  .....    .    . 

For  beams  restrained  at  both  ends,  and  carrying  a  uniformly  distributed  load,  W, 


S  pi 


For  continuous  girders  of  two  equal  spans,  each  carrying  a  uniformly  distributed 
load,  W,  on  each  span, 


.  ...... 

For  continuous  girders  of  three  equal  spans,  each  carrying  a  uniformly  distributed 
load,  W,  on  each  span, 


The  product  Sjp  may  be  obtained  from  Table  XVI  A  for  any  desired  percentage 
of  steel.  Thus  for  p  =  .007,  S  p  j  =  74,  neglecting  fractions. 

Check  Formulas.  —  Formulas  (10)  and  (n)  are  convenient  for  testing  the  strength 
of  a  reinforced  concrete  beam  to  determine  whether  the  external  fibre  stresses  C  and  S, 
in  the  concrete  and  steel  respectively,  are  within  the  limits  set  by  the  specifications. 

'      ' 


The  same  notation  applies  to  these  formulas  as  was  explained  under  Table  XVI  A. 
Table  XVI  A  can  be  used  for  obtaining  values  of  k  and  j  for  any  value  of  C  r,  and  its 
use  is  limited  to  C  =  500  only  for  obtaining  values  of  5  and  the  product  S  p  j.  The 
designer  should,  however,  be  cautioned  as  to  the  use  of  the  effective  depth,  d,  of  the 
beam,  which  extends  only  to  the  plane  of  the  steel  and  does  not  include  the  one  or 
two  inches  of  concrete  which  are  placed  below  the  steel. 

EXAMPLE. — In  checking  a  beam  having  a  span  of  10  ft.,  height  of  20  ins.,  width 
of  9  ins.,  reinforced  with  4-5/8  inch  round  rods  placed  2  ins.  from  the  bottom  of  the 

[205] 


Handbook  for  Cement  and  Concrete  Users 

beam,  and  carrying  a  uniformly  distributed  load  of  12,000  pounds,  including  its  own 
weight,  it  is  required  to  find  whether  the  unit  fibre  stresses  in  the  concrete  and  steel 
are  within  safe  limits. 

Solution.—  From  (i)  M  =  1/8  Wl  =  1/8  X  12,000  X  10  =  15,000  ft.-lbs.  =  180,- 
ooo  inch-pounds. 

d  =  20  —  2  =  18  ins.     b  d  =  9  X  18  =  162  sq.  ins. 
b  d2  =  162  X  18  =  2,916  cu.  ins. 

Area  of  steel  reinforcement,  A  =  4  X  .7854  X  (5/8)2  =  1.227  scl'  ms 

Percentage  of  steel  p  =  1.227  ~^"  IO^  =  -0075. 

From  Table  XVI  A  for  p  —  .0075,  k  =  .345  and  /  =  .886 

2  X  180,000 
From  (,«,)  C  =  ,345  x  ,886  x  a>9,6  -  4<H  Ita.  per  sq.  m. 

From  (i,)  5  =  ^8°8°°°x  2>i6  =  9,29°  Ibs.  per  sq.  in. 


These  are  below  the  limits  of  500  for  concrete  and  16,000  for  steel  and  are,  therefore, 
safe  values. 

Design  of  a  Rectangular  Reinforced  Concrete  Beam.  —  The  dimensions  of  a  hor- 
izontal reinforced  concrete  beam  of  rectangular  section  may  be  accurately  determined 
by  observing  the  following  order  of  computations: 

(1)  Assume  safe  values  for  C,  S,  and  r.     Values  permitted  under  the  provisions 
of  the  New  York  building-code,  are  as  follows: 

C  =  500,  S  =  16,000,  and  r  —  12. 

(2)  Prepare  a  table  giving  values  of  5*  and  the  product  S  p  j  for  different  percent- 
ages of  steel,  p.      Table  XVI  A  of  this  chapter  gives  these  values  for  percentages   of 
steel  ranging  from  .005  to  .02  of  the  area  of  the  section,  based  on  C  =  500  and  r  =  12. 

(3)  Determine  the  amount  and  position  of  the  loads  supported  by  the  beam,  in- 
cluding the  estimated  weight  of  the  beam  itself. 

(4)  Compute  the  amount  and  position  of  the  maximum  bending  moment,  M,  at 
any  section  of  the  beam,  as  explained  in  the  earlier  part  of  this  chapter. 

(5)  Assume  a  percentage  of  steel,  p,  and  note  whether  the  corresponding  value  of 
S,  in  the  table,  is  within  the  specified  limits.     The  values  of  p,  most  commonly  used, 
are  from  .007  to  .012. 

For  example,  in  Table  XVI  A  for  p  =  .010,  the  corresponding  value  of  S  is  9600, 
which  is  well  below  the  limit  of  16,000  and  therefore  a  safe  unit  stress  for  steel  according 
to  the  New  York  building-code. 

(6)  Pick  out  the  corresponding  value  of  the  product  S  p  j  from  the  table  for  use 

in  the  formula,  b  d2  =  —  —  . 


For  example,  in  Table  XVI  A,  for  p  =  .010,  S  p  j  —  83.7. 

(7)  Assume  a  value  for  the  breadth  of  the  beam,  b,  and  compute  the  corresponding 

value  of  the  effective  depth,  d,  using  the  formula  b  d2  =  -^  —  ..     If  necessary  try  several 

values  of  b  in  order  to  obtain  the  best  proportions  of  depth  to  breadth.  The  best 
shaped  beam  is  one  in  which  I)  lies  between  1/2  d  and  3/4  d.  b  should  not  be  less  than 
1/24  of  the  span,  while  d  should  not  exceed  1/8  of  the  span. 

[206]  • 


Explanation  of  the  Theory 


(8)  Compute  the  sectional  area  of  the  steel  from  the  formula  A  =  p  b  d.     The 
area  A  should  be  distributed  over  several  bars.     Thus  for  p  =  .0095,  the  area  of  steel 
required  in  a  beam  of  12  x  20  ins.  is 

A  =  .0095  X  12  X  20  =  2.28  sq.  ins.  area  of  steel. 

If  3/4  inch  square  bars  are  employed,  the  area  of  each  bar  will  be  3/4  X  3/4  =  9/16 
sq.  ins.,  and  the  number  of  bars  required  will  be  2.28  -f-  9/16  =  4. 

The  breadth  of  the  beam  should  be  sufficient  for  the  spacing  of  the  bars.  A  mini- 
mum clear  spacing  of  at  least  i  1/2  diameters  should  be  provided  with  an  equal  distance 
between  the  outside  rod  and  the  surface  of  the  beam. 

Sufficient  rods  should  be  employed,  so  that  the  diameter  of  each  rod  will  not  exceed 
one  two-hundredths  of  the  span. 

The  length  of  rod  on  either  side  of  the  point  of  maximum  bending  moment  should 
be  at  least  eighty  diameters  for  plain  and  fifty  diameters  for  deformed  bars. 

(9)  Check  the  assumed  weight  of  the  beam. 

EXAMPLE.  —  It  is  required  to  find  the  dimensions  and  reinforcement  required  for  a 
reinforced  concrete  beam,  supported  at  each  end,  which  will  carry  a  uniformly  dis- 
tributed weight  of  15,000  pounds  over  a  span  of  14  feet,  in  conformity  with  the  require- 
ments of  the  New  York  building-code. 

Solution.  —  (i)  According  to  the  requirements,  C  =  500;  r=  12;  and  S  —  16,000. 

(2)  Table  XVI-A  of  this  chapter  may  be  employed  in  this  design. 

(3)  Assume  the  weight  of  the  beam  to  be  3,700  pounds;   then  the  total  load  to  be 
supported  will  be  15,000  +  3,700  =  18,700  pounds. 

(4)  Since  the  weight  is  uniformly  distributed,  the  maximum  bending  moment  will 
be  at  the  centre  of  the  span,  and  its  value  be  given  by  the  formula: 

M  =  1/8  /  (W+W)  or  substituting 
M  =  1/8  X  18,700  Ibs.  X  1  68  ins.,  or 
M  =  392,700  inch-pounds. 

(5)  Assume  a  value  of  p  =  .0095  for  the  percentage  of  steel.     Then  from  Table 
XVI  A,  5  will  be  between  the  values  of  10,250  and  9,600  pounds  per  sq.  inch,  which  is 
well  below  the  limiting  value  of  16,000  pounds  required  for  safe  design  according  to 
the  conditions,  and  is  therefore  safe. 

(6)  The  value  of  the  product  .S  p  j,  corresponding  to  p  =  .0095,  will  lie  between 
the  values  80.9  and  83.7  in  Table  XVI  A,  and  for  practical  purposes  can   be  taken 
as  midway  between  these  values  or 


(7)  Assume  a  breadth,  &,  as  3/5  of  the  depth,  or  b  =  3/5  d,  and  substituting  in 
the  formula  bd  2  =  -  —  :,  we  have 


Solving  for  d,  we  have  d  =  20  ins.,  and  since  b  =  3/5  d,  therefore  b  =  3/5  X  20  or  12 
ins. 

(8)  Since  p  =  .0095,  A  the  area  of  the  steel  reinforcement  will  be  .0095  b  d  or 

A  =  .0095  X  12  X  20,  or 
A  =  2.28  sq.  ins. 

If  3/4  inch  square  bars  are  employed,  the  number  of  bars  required  will  be  2.28  -f- 
(3/4  X  3/4)  =  4  plus  a  very  small  fraction  which  can  be  ignored. 

(9)  The  beam  was  assumed  to  weigh  3,700  pounds,  and  if  the  actual  design  shows 
it  to  be  materially  heavier,  a  revision  must  be  made. 

[207] 


Handbook  for  Cement  and  Concrete  Users 

The  volume  of  the  beam  in  cu.  ft.,  as  designed,  is: 

;  12  X  22* 

14  X  — — —  =  25.7  cu.  ft. 
144 

If  the  concrete  is  a  dense  mixture,  weighing  144  pounds  per  cu.  ft.,  its  weight  will 
be  144  X  25.7  =  3,700  pounds  as  assumed.  Having  checked  the  weight,  the  design 
should  now  be  investigated  to  determine  whether  it  is  in  conformity  with  the  following 
practical  considerations. 

(a)  Whether  the  breadth  is  between  the  limits  of  1/2  and  3/4  the  depth. 

(b)  Whether  the  breadth  is  greater  than  1/24  of  the  span. 

(c)  Whether  the  diameter  of  the  bars  is  less  than  1/200  of  the  span. 

(d)  Whether  the  breadth  is  sufficient  to  provide  at  least  i  1/2  diameters  spacing 
between  the  bars,  and  between  the  bars  and  the  sides  of  the  beam. 

Summarizing  the  results  of  the  design,  we  have 

Total  depth  of  beam,  22  ins. 

Depth  to  plane  of  steel,  20  ins. 

Breadth  of  beam,  12  ins. 

Reinforcement  4-3/4  inch  medium  steel  square  bars. 

Design  of  Web  Reinforcement  or  Stirrups. — Stirrups  are  required  when  the 
vertical  shear  exceeds  a  safe  value  for  concrete.  The  vertical  shear  at  any  section  of 
a  beam  is  equal  to  the  reaction  at  a  support  diminished  by  the  sum  of  the  intervening 
loads.  Thus  in  the  preceding  example,  each  of  the  end  supports  carries  one-half  of 
the  load  or  9,350  pounds,  and  the  vertical  shear  at  a  support  will  also  have  this  value. 

Shearing  stresses  are  not,  however,  uniformly  distributed  over  the  cross-section, 
and  the  maximum  value  is  approximately  8/7  of  the  average  value,  while  the  unit 
stress  or  stress  per  sq.  inch  of  cross-section,  is  found  by  dividing  the  maximum  value 
by  the  area  of  the  section,  or 

v=8/7V/bd (23) 

in  which  v  is  the  unit  shearing  stress  and  V  the  total  vertical  shear  produced  by  the 
loads  at  any  section  of  a  beam,  having  a  breadth,  b,  and  effective  depth,  d. 

Concrete  can  safely  sustain  a  unit  shearing  stress,  v,  of  from  30  to  50  pounds  per 
sq.  inch,  and  if  this  value  is  exceeded,  stirrups  must  be  provided  to  take  care  of  the 
excess.  In  large  and  important  girders  stirrups  should,  however,  always  be  provided 
even  if  the  shearing  stress  is  low. 

In  the  previous  example,  the  maximum  shear  at  either  support  is  9,350  pounds,  and 
substituting  in  formula  (23),  with  b  =  12,  and  d  =  20  ins.,  we  have 

8  Q,^O  * 

v  =  y  x  i2x'2o  =  44*5     per  sq* m>' 

which  is  large  enough  to  necessitate  the  use  of  stirrups  in  a  conservative  design. 

Design  of  Stirrups. — Where  the  unit  shearing  stress,  v,  is  in  excess  of  a  safe  value 
for  concrete,  say  over  30  pounds  per  sq.  in.,  stirrups  should  be  provided,  or  the  rods 

8      V 
bent  up  at  intervals,  beginning  at  the  point  where  —  r-j  exceeds  30. 

Let  5  =  the  horizontal  spacing  of  the  stirrups  along  the  beam,  and  let 

F'  =    y   V-3obd         .     \       .       ....       (24) 

*  20  ins,,  plus  2  ins.  below  the  plane  of  the  steel. 


Explanation  of  the  Theory 


Call  i)'  the  average  intensity  of  the  shear  over  the  same  section,  that  must  be  carried 
by  the  stirrups,  then 

V 


and  the  total  tension  in  the  stirrups  will  be 

T  =  vf 
while  the  sectional  area  required  for  the  steel  will  be 


V  * 
T  =  vf  b  s  =  --      ........     (26) 


If  the  stirrups  are  inclined  instead  of  vertical,  the  distance,  s,  is  the  perpendicular 
distance  between  the  inclined  members.  Where  the  stirrups  are  perpendicular  to  the 
horizontal  members,  s,  to  be  effective,  should  not  exceed  1/2  the  depth  of  the  beam, 
and  where  inclined  at  an  angle  of  45°  should  not  exceed  3/4  of  the  depth.  S,  the 
unit  stress  in  the  steel,  should  not  exceed  10,000  Ibs.  per  sq.  in. 

For  example,  if  the  vertical  shear  at  the  end  section  of  a  beam,  24  ins.  deep  by 
14  ins.  wide,  is  13,125  Ibs.,  and  two  square  rods  are  bent  up  vertically  at  the  centre 
of  the  section,  the  section  being  12  inches  long,  it  is  required  to  find  the  sectional 
area  required  for  the  steel,  the  unit  shearing  stresses  being  taken  at  30  and  10,000  Ibs. 
per  sq.  in.,  respectively  in  the  concrete  and  steel. 

From  (24)  V  =  —  V  -  30  b  d  or 

V  =  y  X  13,125  -  (30  X  14  X  24)  =  4,920  Ibs. 

,      v  V  S  4,02O  X  12 

From  (27)  A  =  -—  or  A  =  -22  -  —  —  =  0.246  sq.  ins. 
Sd  10,000  X  24 

If  two  square  rods  are  employed,  the  area  of  each  should  be  0.123  sq.  ins.,  or  the  dimen- 
sions 3/8  X  3/8  ins.  In  general  from  three  to  four  pair  of  stirrups  should  be  used  at 
each  end  of  the  beam,  according  to  the  span. 

Bond  Strength  Between  Steel  and  Concrete.-  —  For  the  purposes  of  design  this 
should  not  exceed  50  pounds  per  sq.  in.  of  steel  area  and  if  this  amount  be  exceeded, 
the  area  of  the  steel  must  be  increased,  either  by  increasing  the  percentage  of  steel  or 
the  number  of  bars  or  both. 

The  bond  between  steel  and  concrete  may  be  tested  by  the  approximate  formulas 

*-  f  -5-  .........  c-o 

and  u  =  —       ..........     (29) 

in  which  V  =  the  maximum  vertical  shear  produced  by  the  loading,  U  the  bond  stress 
per  unit  length  of  beam,  u  the  bond  stress  per  unit  area,  say  50  Ibs.  per  sq.  in.,  and  o 
the  sum  of  the  perimeters  of  the  steel  sections. 

In  the  example  worked  out  on  page  207  the  reaction  at  the  supports  was  found  to 
be  9,350  Ibs.,  which  is  equal  to  V,  while  d=2o  ins.,  and  the  sum  of  the  perimeters  of 
the  steel  sections,  o,  for  4-3/4  inch  square  bars  is  4  x  4  x  3/4=  12  ins.  Hence  from  (28) 


from  (29),  u  =  534  ~  12  =  44.5  Ibs.  per  sq.  inch,  which  is  below  the  limiting  value 
of  50  Ibs.  per  sq.  in.     Hence  the  design  is  satisfactory  as  regards  bond. 

14  [209] 


Handbook  for  Cement  and  Concrete  Users 

Design  of  Reinforced  Concrete  Slabs. — For  the  strength  of  slabs,  the  same  formulas 
apply  as  for  beams.  The  slab  may  be  treated  as  a  rectangular  beam  of  unusual  width, 
or  it  may  be  considered  as  a  series  of  beams  set  one  alongside  of  another,  of  a  width 
equal  to  the  spacing  of  the  reinforcing  bars,  using  one  rod  for  each  beam. 

In  the  case  of  square  slabs,  the  reinforcement  should  be  of  equal  amount  in  the  two 
directions.  It  may  be  calculated  on  the  assumption  that  one-half  the  load  is  carried 
by  each  system  of  reinforcement.  The  concrete  is  proportioned  for  one  system  only, 
or  one-half  the  load,  as  the  stresses  due  to  the  two  systems  are  at  right  angles  to  each 
other,  and  the  stresses  in  one  direction  do  not  weaken  the  concrete  with  respect  to 
stresses  in  the  other. 

In  the  case  of  oblong  slabs,  the  relative  amount  of  load  carried  by  the  longitudinal 
system  is  so  small  that  it  cannot  be  considered  in  the  design. 

While  longitudinal  reinforcement  is  of  little  value  in  carrying  loads,  a  small  amount 
is  nevertheless  often  desirable  in  preventing  cracks  and  in  binding  the  entire  structure 
together.  For  this  purpose  1/4  or  3/8  inch  rods  spaced  about  two  feet  apart,  are 
frequently  used.  Metal  fabrics  are  also  commonly  employed  for  reinforcing  slabs. 
The  successive  steps  to  be  followed  in  the  design  of  a  slab  are  explained  and  illustrated 
in  the  preceding  chapter. 

T'-beams  generally  occur  in  the  practice  where  a  slab  and  its  supporting  girder  are 
cast  at  the  same  time,  as  in  floor  construction. 

The  width  of  slab  that  may  be  taken  as  part  of  the  beam  is  generally  limited  to 
from  four  to  six  times  the  width  of  the  stem,  but  in  any  case  the  width  of  slab  must 
not  be  taken  as  more  than  the  distance  between  beams. 

Where  the  neutral  axis  is  not  below  the  junction  of  web  and  flange,  T-beams  may 
be  designed  by  the  same  formulas  as  are  used  for  simple  beams  by  substituting  for  the 
actual  T-section  the  area  found  by  multiplying  the  breadth  of  the  flange  by  the  effective 
depth  of  the  beam. 

Such  a  beam,  however,  must  be  very  carefully  checked  for  shear  between  the  flange 
and  web,  for  bond  between  the  steel  and  concrete,  and  for  negative  bending  moments 
at  the  supports,  which,  if  present,  would  produce  tension  in  the  slab  at  the  top  of  the 
beam  and  compression  in  the  narrow  stem  at  the  bottom  of  the  beam. 

For  a  thorough  treatment  of  the  design  of  T-beams,  double-reinforced  beams, 
arches,  etc.,  the  reader  is  referred  to  Turneaure  and  Maurer's  "Principles  of  Reinforced 
Concrete  Construction,"  and  other  standard  text-books  on  the  subject.  Further 
practical  principles  of  design  in  so  far  as  they  relate  to  foundations,  retaining  walls, 
piers,  and  abutments,  building  construction,  etc.,  will  be  found  in  the  appropriate 
chapters  of  this  book. 

RECOMMENDED    PRACTICE    FDR    DESIGNING    REINFORCED 
CONCRETE    STRUCTURES* 

(i)  The  materials  and  workmanship  for  reinforced  concrete  should  meet  the  re- 
quirements of  the  "  Specifications  for  Plain  and  Reinforced  Concrete  "  presented  in 
this  report  of  the  Committee  on  Masonry. 

The  concrete  recommended  for  general  use  is  a  mixture  of  one  part  of  cement  to 
six  parts  of  fine  and  coarse  aggregates.  A  richer  mixture  will  be  found  advantageous 
for  special  conditions. 

*  From  the  report  of  the  committee  on  Masonry  of  the  American  Railway  Engineering 
and  Maintenance  of  Way  Association,  presented  at  their  annual  convention  in  Chicago, 
1910. 

[210] 


Explanation  of  the  Theory 


(2)  The  dead  load  is  to  include  the  estimated  weight  of  the  structure  and  all  other 
fixed  loads  and  forces  acting  upon  the  structure. 

(3)  The  live  load  is  to  include  all  variable  and  moving  loads  or  forces  acting  upon 
the  structure  in  any  direction. 

(4)  As  the  working  stresses  herein  recommended  are  for  static  loads,  the  dynamic 
effect  of  moving  loads  is  to  be  added  to  the  live  load  stresses. 

(5)  The  span  length  for  beams  and  slabs  is  to  be  taken  as  the  distance  from  centre  to 
centre  of  the  supports,  but  not  to  exceed  the  clear  span  plus  the  depth  of  beam  or  slab. 

(6)  The  internal  stresses  are  to  be  calculated  upon  the  basis  of  the  following  as- 
sumptions: 

(a)  A  plane  section  before  bending  remains  plane  after  bending. 
(&)  The  distribution  of  compressive  stresses  in  members  subject  to  bending  is 
rectilinear. 

(c)  The  ratio  of  the  moduli  of  elasticity  of  steel  and  concrete  is  12.* 

(d)  The  tensile  stresses  in  the  concrete  are  neglected  in  calculating  the  moment 
of  resistance  of  beams. 

(e)  The  initial  stress  in  the  reinforcement  due  to  contraction  or  expansion  in  the 
concrete  is  neglected. 

(/)  The  depth  of  a  beam  is  the  distance  from  the  compressive  face  to  the  centroid 
of  the  tension  reinforcement. 

(g)  The  effective  depth  of  a  beam  at  any  section  is  the  distance  from  the  centroid 
of  the  compressive  stresses  to  the  centroid  of  the  tension  reinforcement. 

(ti)  The  maximum  shearing  unit  stress  in  beams  is  the  total  shear  at  the  section 
divided  by  the  product  of  the  width  of  the  section  and  the  effective  depth  at  the  section 
considered.  This  maximum  shearing  unit  stress  is  to  be  used  in  place  of  the  diagonal 
tension  stress  in  calculations  for  web  stresses. 

(*)  The  bond  unit  stress  is  equal  to  the  vertical  shear  divided  by  the  product  of  the 
total  perimeter  of  the  reinforcement  in  the  tension  side  of  the  beam  and  the  effective 
depth  at  the  section  considered. 

(6)  In  concrete  columns  the  concrete  to  a  depth  of  i$  in.  is  to  be  considered  as  a 
protective  covering  and  is  not  to  be  included  in  the  effective  section. 

(7)  When  the  maximum  shearing  stresses  exceed  the  value  allowed  for  the  concrete 
alone,  web  reinforcement  must  be  provided  to  aid  in  carrying  the  diagonal  tension 
stresses.     This  web  reinforcement  may  consist  of  bent  bars,  or  inclined  or  vertical 
members,  attached  to  or  looped  about  the  horizontal  reinforcement.     Where  inclined 
members  are  used,  the  connection  to  the  horizontal  reinforcement  shall  be  such  as  to 
insure  against  slip. 

"  In  the  calculation  of  web  reinforcement  when  the  concrete  alone  is  insufficient  to 
take  the  diagonal  tension,  the  concrete  may  be  counted  upon  as  carrying  one-third  of 
the  shear.  The  remainder  is  to  be  provided  for  by  means  of  metal  reinforcement 
consisting  of  bent  bars  or  stirrups,  but  preferably  both.  The  requisite  amount  of  such 
reinforcement  may  be  estimated  on  the  assumption  that  the  entire  shear  on  a  section, 
less  the  amount  assumed  to  be  carried  by  the  concrete,  is  carried  by  the  reinforcement 
in  a  length  of  beam  equal  to  its  depth." 

(8)  The  following  recommended  working  stresses,  in  pounds  per  square  inch  of 
section,  are  for  use  in  concrete  of  such  quality  as  to  be  capable  of  developing  an  average 

*  The  unit  stresses  as  recommended  in  the  report  were  higher  than  these  values, 
which  have  been  reduced  in  conformity  with  the  fibre  stresses  employed  in  other  por- 
tions of  the  chapter. 


Handbook  for  Cement  and  Concrete  Users 

compress! ve  strength  of  at  least  2,000  Ibs.  per  square  inch,  when  tested  in  cylinders  8 
in.  in  diameter  and  16  in.  long,  and  28  days  old,  under  laboratory  conditions  of  manu- 
facture and  storage,  the  mixture  being  of  the  same  consistency  as  is  used  in  the  field. 

Structural  steel  in  tension . 14,000 

High  carbon  steel  in  tension 17,000 

t  Steel  in  compression,  12  times  the  compressive  stress  in  the  surrounding  con- 
crete 

Concrete  in  bearing  where  the  surface  is  at  least  twice  the  loaded  area 700 

f  Concrete  in  direct  compression,  without  reinforcement  on  lengths  not  ex- 
ceeding twelve  times  the  least  width    350 

t  Concrete  in  direct  compression  with  not  less  than  i  per  cent,  nor  over  4  per 
cent  longitudinal  reinforcement  on  lengths  not  exceeding  twelve  times  the 

least  width 350 

f  Concrete  in  compression,  on  extreme  fibre  in  cross  bending 500 

f  Concrete  in  shear,  where  the  shearing  stress  is  used  as  the  measure  of  web 

stress    30 

NOTE. — The  limit  of  shearing  stresses  in  the  concrete,  even  when  thoroughly 

reinforced  for  shear  and  diagonal  tension,  should  not  exceed 120 

f  Bond  for  plain  bars 50 

f  Bond  for  drawn  wire 30 

t  Bond  for  deformed  bars,  depending  upon  form 80-1 20 

NOTE:  Chapters  XVII  and  XVIII  differ,  in  that,  the  former  chapter  is  applicable 
only  to  the  column  and  to  the  special  case  of  the  simple  horizontal  beam  carrying  a 
uniformly  distributed  load,  while,  in  the  latter  chapter,  the  methods  are  general  and 
applicable  to  beams  loaded  in  any  manner.  The  methods  of  design  are,  however, 
identical  in  both  chapters,  and  in  order  to  render  each  one  complete  in  itself,  a  certain 
amount  of  matter  has  been  repeated.  It  is  thought  that  the  reading  of  this  chapter 
will  be  rendered  easier  by  first  showing  the  application  of  the  theory  of  design  to  a 
simple  case,  as  was  done  in  Chapter  XVII. 


f  The  unit  stresses  as  recommended  in  the  report  were  in  general  higher  than 
these  values,  which  have  been  reduced  in  conformity  with  the  fibre  stresses  employed 
in  other  portions  of  the  chapter. 

[212] 


CHAPTER  XIX 

SYSTEMS    OF   REINFORCEMENT    EMPLOYED 

Systems  of  Reinforcement  Employed.  —  Different  Forms  of  Rods  and  Bars.  —  Special 
Fabrics  and  Types  of  Reinforcement. 

REINFORCEMENT  is  used  in  a  variety  of  shapes  and  combina- 
tions, nearly  all  of  them  patented,  and  some  of  them  forming  the 
basis  for  so-called  systems. 

All  these  systems  of  reinforcement  have  been  developed  princi- 
pally during  the  last  decade,  each  one  of  them  having  its  adherents 
and  all  of  them  giving  substantial  structures  if  intelligently  em- 
ployed. The  selection  of  the  type  for  any  particular  case  will 
depend  upon  the  nature  of  the  structure,  the  local  conditions,  the 
experience  of  the  designer,  and  often  upon  the  argument  of  the 
salesman.  The  illustrations  will  serve  to  bring  out  the  essential 
features  of  the  different  systems. 

Specifications  for  Reinforcing  Steel.  —  The  quality  of  steel  to 
be  used  for  reinforced  concrete  work  has  received  a  great  deal  of 
attention  from  engineers  and  steel-makers  and  the  rules  given  below 
represent  the  latest  practice  in  this  respect  : 

SPECIFICATIONS  FOR  STEEL  REINFORCEMENT  * 

1.  Steel  shall  be  made  by  the  open-hearth  process.     Rerolled 
material  will  not  be  accepted. 

2.  Plates  and  shapes  used  for  reinforcement  shall  be  of  structural 
steel  only.     Bars  and  wire  may  be  of  structural  steel  or  high  carbon 
steel. 


*  From  the  report  of  the  Committee  on  Masonry  at  the  annual  convention  of  the 
American  Railway  Engineering  and  Maintenance  of  Way  Association,  Chicago,  March 
16,  1910. 


Handbook  for  Cement  and  Concrete  Users 


3.  The  chemical  and  physical  properties  shall  conform  to  the 
following  limits : 


Elements  Considered. 

Structural  Steel. 

High  Carbon  Steel. 

(  Basic 

o  04  per  cent 

o  04  per  cent 

Phosphorus,  max  .  .                        .  .  i 

1  Acid 

o  06  per  cent 

o  06  per  cent 

Sulphur,  maximum  

0.05  per  cent. 

0.05  per  cent. 

Ultimate  tensile  strength. 
Pounds  per  square  inch  

Desired. 
60,000 

Desired. 
88,000 

Elong.,  min  per  cent  in  8"             

2(;% 

20% 

Character  of  Fracture 

Silky 

Silky  or  finely 

Cold  Bends  without  Fracture 

1  80°  flatf 

granular 
1  80°  d  —  4/*t 

4.  The  yield  point  for  bars  and  wire,  as  indicated  by  the  drop  of 
the  beam,  shall  be  not  less  than  60  per  cent  of  the  ultimate  tensile 
strength. 

5.  If  the   ultimate  strength  varies  more  than  4,000  Ibs.   for 
structural  steel  or  6,000  Ibs.  for  high  carbon  steel,  a  retest  shall  be 
made  on  the  same  gauge,  which,  to  be  acceptable,  shall  be  within 
5,000  Ibs.  for  structural  steel,  or  8,000  Ibs.  for  high  carbon  steel, 
of  the  desired  ultimate. 

6.  Chemical     determinations    of   the    percentages   of   carbon, 
phosphorus,  sulphur,  and  manganese  shall  be  made  by  the  manu- 
facturer from  a  test  ingot  taken  at  the  time  of  the  pouring  of  each 
melt  of  steel,  and  a  correct  copy  of  such  analysis  shall  be  furnished 
to  the  engineer  or  his  inspector.     Check  analyses  shall  be  made 
from  finished  material,  if  called  for  by  the  railroad  company,  in 
which  case  an  excess  of  25  per  cent  above  the  required  limits  will  be 
allowed. 

7.  Plates,  Shapes,  and  Bars. — Specimens  for  tensile  and  bending 
tests  for  plates  and  shapes  shall  be  made  by  cutting  coupons  from 
the  finished  product,  which  shall  have  both  faces  rolled  and  both 
edges  milled  to  the  form  of  a  standard  test  specimen;  or  with  both 
edges  parallel;   or  they  may  be   turned  to  a  diameter   of   J    inch 
with  enlarged  ends. 

*  See  paragraphs  n  and  12.     f"  d  =  4}"  signifies  "around  a  pin  whose  diameter  is 
four  times  the  thickness  of  the  specimen." 


Systems  of  Reinforcement  Employed 

8.  Bars  shall  be  tested  in  their  finished  form. 

9.  At  least  one  tensile  and  one  bending  test  shall  be  made  from 
each  melt  of  steel  as  rolled.     In  case  steel  differing  3/8  in.  and  more 
in  thickness  is  rolled  from  one  melt,  a  test  shall  be  made  from  the 
thickest  and  thinnest  material  rolled. 

10.  For  material  less  than  5/16  in.  and  more  than  3/4  in.  in 
thickness  the  following  modifications  will  be  allowed  in  the  require- 
ments for  elongation : 

(a)  For  each  1/16  in.  in  thickness  below  5/16  in.,  a  deduction 
of  2  1/2  will  be  allowed  from  the  specified  percentage. 

(b)  For  each  1/8  in.  in  thickness  above  3/4  in.,  a  deduction  of 
i  will  be  allowed  from  the  specified  percentage. 

11.  Bending  tests  may  be  made  by  pressure  or  by  blows.    Shapes 
and  bars  less  than  one  inch  thick  shall  bend  as  called  for  in  para- 
graph 3. 

12.  Test  specimens  one  inch  thick  and  over  shall  bend  cold 
1 80°  around  a  pin,  the  diameter  of  which,  for  structural  steel,  is 
twice  the  thickness  of  the  specimen,  and  for  high   carbon  steel  is 
six  times  the  thickness  of  the  specimen,  without  fracture  on  the 
outside  of  the  bend. 

13.  Finished  material  shall  be  free  from  injurious  seams,  flaws, 
cracks,  defective  edges,  or  other  defects,  and  have  a  smooth,  uniform, 
and  workmanlike  finish. 

14.  Every  finished  piece  of  steel  shall  have  the  melt  number  and 
the  name  of  the  manufacturer  stamped  or  rolled  upon  it,  except 
that  bar  steel  and  other  small  parts  may  be  bundled  with  the  above 
marks  on  an  attached  metal  tag. 

15.  Material,  which,  subsequent  to  the  above  tests  at  the  mills, 
and  its  acceptance  there,  develops  weak  spots,  brittleness,  cracks 
or  other  imperfections,  or  is  found  to  have  injurious  defects,  will  be 
rejected  and  shall  be  replaced  by  the  manufacturer  at  his  own  cost. 

1 6.  All  reinforcing  steel  shall  be  free  from  excessive  rust,  loose 
scale,  or  other  coatings  of  any  character,  which  would  reduce  or 
destroy  the  bond. 

Types  of  Reinforcement. — The  reinforcement  consists  of  steel 
in  one  or  more  of  the  following  forms : 

1.  Round  or  square  rods. 

2.  Twisted  or  deformed  rods,  .     j 

[215] 


Handbook  for  Cement  and  Concrete  Users 

3.  Unit  systems. 

4.  Woven  wire,  expanded  metal,  welded,  or  other  fabrics. 

5.  Spiral  reinforcement  for  columns. 

6.  Various  patented  systems. 

The  plain  bars  either  depend  upon  the  adhesion  of  the  steel 
and  concrete  for  the  action  of  the  two  materials  in  combination,  or 
the  ends  of  rods  are  anchored  in  the  concrete  for  the  purpose  of 
developing  their  full  tensile  strength. 

In  the  deformed  bars  the  adhesion  of  the  concrete  to  the  steel 
is  supplemented  by  a  mechanical  bond  due  to  the  shape  of  the  bar. 
The  following  bars  are  among  the  best  known  of  this  class : 

1.  Ransome  twisted  bars  are  made  of  square  bars  twisted  cold. 

2.  Johnson  corrugated  bar  in  which  the  mechanical  bond  is 
effected  by  a  series  of  corrugations  on  the  sides  of  a  square  rod. 

3.  Diamond  bar  which  is  a  round  bar  crossed  by  diagonals. 

4.  Cold  twisted  lug  bar,  which  is  a  Ransome  bar  having  small 
projections  at  intervals. 

5.  Cup  bar  in  which  the  mechanical  bond  is  effected  by  a  series 
of  cups. 

6.  DeMan  undulated  bar. 

7.  Universal  type  corrugated  bar. 

8.  The  Kahn  and  Golding  bars  which  are  provided  with  attached 
shear  members. 

Unit  Systems,  Fabrics,  and  Spiral  Reinforcement. — In  the 
unit  systems,  the  reinforcement,  including  the  tension  rods  and 
stirrups,  are  so  tied  and  framed  together  that  after  being  placed 
in  the  forms  the  possibility  of  shifting  their  positions  with  re- 
spect to  the  other  surfaces  of  the  beam,  or  to  one  another,  is 
practically  removed. 

Steel  fabrics  are  largely  employed  in  slab  and  floor  construction, 
also  in  conduits,  tanks,  foundations,  etc. 

Spiral  wrappings  for  columns  are  employed  for  the  purpose  of 
permitting  a  higher  unit  stress  to  come  upon  the  concrete  than 
could  safely  be  used  without  such  reinforcement.  The  spirals 
have  the  effect  of  confining  the  concrete  and  preventing  it  from 
bulging  or  splitting. 

Special  Systems  of  Reinforcement. — The  following  are  among 
the  so-called  special  systems  of  construction; 

[216] 


Systems  of  Reinforcement  Employed 

The  Expanded  Metal  System* — Expanded  metal  is  made  from 
mild  steel,  having  an  ultimate  resistance  of  48,000  pounds  per 
square  inch  and  an  elongation  of  21  per  cent  in  a  length  of  8  inches. 
It  is  manufactured  from  flat  plates  of  thickness  varying  from  1/4  to 
about  1/8  of  an  inch,  and  when  expanded,  the  usual  meshes  are 
from  6  inches  to  3  inches  in  width.  The  operation  of  making  it 
consists  in  placing  the  sheets  vertically,  resting  on  their  edges. 
They  are  then  slotted  and  pulled  out  at  one  operation.  After  being 
slotted,  they  are  drawn  out  laterally  so  that  the  width  of  the 
finished  sheet  is  in  reality  produced  from  the  height  of  the 
original  plate  when  placed  with  its  edge  downward.  The  expan- 
sion effect  varies  from  about  6  to  12  times  the  original  width 
of  the  plate.  However,  no  alteration  is  made  in  the  length, 
the  strands  being  consequently  somewhat  stretched.  A  por- 
tion is  left  uncut,  thereby  forming  a  strong  "selvedge77  edge. 
It  has  been  found  that  the  ultimate  strength  is  increased  from 
48,000  to  about  63,000  pounds  per  square  inch  through  the 
operation  of  expanding.  Expanded  metal  is  mainly  used  for  slab 
construction,  although  in  a  few  instances,  it  has  also  been  used 
in  the  construction  of  beams. 

The  Clinton  System. — A  reinforcing  for  concrete  construction 
of  all  kinds  which  is  being  extensively  used  in  this  country  is  the 
electrically  welded  fabric  manufactured  by  the  Clinton  Wire  Cloth 
Company,  of  Clinton,  Mass.  The  late  Frank  E.  Kidder  stated 
that  from  a  theoretical  standpoint  at  least  this  fabric  would  seem 
to  offer  the  ideal  reinforcement  for  slab  construction,  as  the  carrying 
wires  may  be  varied  both  in  size  and  spacing  to  give  the  necessary 
area  for  any  given  weight  and  span.  The  distributing  or  cross 
wires  may  likewise  be  varied  in  the  same  way.  The  direction  of 
the  wires  coincides  with  the  line  of  stress  so  that  there  is  no  tendency 
to  distort  the  rectangle  of  the  mesh. 

As  this  fabric  comes  in  3oo-foot  rolls  it  can,  in  a  building  say, 
for  instance,  200  feet  long,  be  secured  at  the  front  or  rear  and  carried 
through  the  entire  distance  without  a  break.  Owing  to  the  con- 
tinuous bond  the  reinforcing  is  equally  strong  at  all  points  and  the 
reinforcing  members  are  exactly  spaced  2,  3,  or  4  inches  apart  as 

*  Description   adapted   partly  from  American  Cement  Company's  publication,  by 
Walter  Muller. 


Handbook  for  Cement  and  Concrete  Users 

the  case  may  be.  This  spacing  is  exact;  it  is  established  by  ma- 
chinery and  is  not  subject  to  the  carelessness  of  employees. 

The  Kahn  System. — This  system,  which  is  being  advocated  by 
the  Trussed  Concrete  Steel  Co.,  of  Detroit,  Mich.,  embodies  the 
use  of  what  is  known  as  the  Kahn  trussed  steel  bar.  This  bar  is 
rolled  of  a  diamond  section  with  projecting  wings  on  either  side. 
The  wings  are  slotted  off  along  the  edge  of  the  diamond  for  certain 
distances  and  are  bent  up  to  an  angle  of  about  forty-five  degrees  to 
form  the  reinforcements  resisting  the  shearing  stresses.  They  are 
consequently  rigidly  connected  to  the  main  bottom  bars. 

The  three  principal  advantages  claimed  for  the  employment  of 
this  form  of  reinforcement  are : 

1.  The  reinforcement  in  the  vertical  plane  is  rigidly  attached  to 
the  main  horizontal  member  and  lies  in  such  a  direction  as  to  cross 
at  right  angles  the  lines  of  rupture. 

2.  The  design  of  the  diagonals  economizes  in  the  amount  of 
metal  required  and  enables  same  to  be  placed  with  a  maximum 
amount  of  speed  and  economy. 

3.  Absolute  fireproofness  of  structures  is  the  result  because  this 
reinforcement  does  not  depend  upon  the  lower  part  of  the  concrete, 
which  is  affected  by  fire. 

The  Hennebique  System. — This  system,  which  is  one  of  the  best 
known  and  most  extensively  used  in  Europe,  was  brought  out  in 
1892  by  M.  Hennebique,  who  was  one  of  the  first  to  introduce  the 
reinforced  concrete  beam  and  is  sometimes  mistakenly  designated 
as  its  original  inventor. 

The  floors,  according  to  the  Hennebique  system,  are  formed  in 
several  ways,  the  most  commonly  employed  being  the  flat  single  floor 
with  exposed  beams.  The  floor  rods  are  in  two  series,  one  bent  up 
to  pass  over  the  support  near  the  upper  surface  of  the  slab  and  the 
other  set  straight  throughout  and  embedded  near  the  lower  surface. 

The  Hinchman-Renton  System. — While  plain  iron  rods  have 
never  been  known  to  slide  or  slip  in  concrete  yet  on  account  of  the 
possibility  that  the  sliding  resistance  along  the  embedded  steel  will 
decrease  in  time  under  frequently  repeated  loads,  American  en- 
gineers have  deemed  it  wise  to  use  the  reinforcing  steel  in  such  shape 
that  sliding  in  the  concrete  will  be  impossible  without  tearing  and 
crushing. 


Systems  of  Reinforcement  Employed 

In  seeking  for  material  that  would  satisfactorily  supply  the  tensile 
strength  required  by  floor  slabs  it  occurred  to  Mr.  J.  B.  Hinchman 
of  the  Hinchman-Renton  Company,  Denver,  Colorado,  that  ordinary 
barbed  wire  would  afford  the  necessary  reinforcement. 

Roebling  System. — The  Roebling  system  is  employed  in  connec- 
tion with  a  structural  steel  frame  of  I-beam  or  girder  construction. 

For  all  flat  construction  of  floors,  the  reinforcing  system  used 
consists  of  flat  bars  placed  upon  edge,  secured  at  the  ends  to  the 
steel  beams  and  bridged  with  bar  separators.  The  object  of  the 
edgewise  position  of  the  bars  is  the  increased  protection  thus  secured 


FIG.  58. — The  Hennebique  System  of  Reinforced  Concrete  in  Building  Construction. 

to  the  reinforcing  steel.  With  this  type  of  floor  the  structural  steel 
frame  is  generally  completely  encased  with  concrete. 

For  light  roof  construction  where  the  steel  work  need  not  be 
protected,  a  continuous  slab  is  built  over  the  beams,  reinforced  with 
flat  steel  bars,  3-16  by  11/4  inches,  placed  edgewise  and  held  in 
position  by  spacers. 

For  floor  construction  the  Roebling  Company  also  uses  segmental 
arches  of  cinder  concrete  laid  upon  permanent  stiffened  wire  lath 
centering,  or  upon  wood  centering  which  is  carried  on  steel  tees  and 
supported  by  the  steel  I-beams  of  the  floor  system,  which  are  gener- 
ally placed  about  7  feet  on  centres.  In  this  system  the  material  is 

[219] 


Handbook  for  Cement  and  Concrete  Users 

placed  upon  the  centering  without  puddling  or  tamping,  in  order  to 
obtain  a  light  porous  concrete  of  high  fire-resisting  quality. 

The  Turner  Mushroom  System.— The  promoter  of  this  system, 
Mr.  C.  A.  P.  Tuiner,  claims  that  in  warehouse  work  it  is  perfectly 
feasible  to  put  up  a  building  with  columns  at  1 6-foot  centres  with  a 


•5111 


FIG.  sg.— The  Merrick  Floor  System. 
6/rtfer  fleam  *<*>  Gti/o 


FIG.  60. — The  Cummings  System. 

floor  of  7  1/2  in.  rough  slabs,  using  no  ribs  at  all,  and  test  it  with 
800  Ib.  per  sq.  ft.,  without  injury  to  the  construction.  Furthermore 
he  claims  that  it  can  be  put  up  at  less  cost  without  the  ribs,  and  will 
require  less  metal,  as  the  load  will  travel  more  directly  to  the  sup- 
ports, instead  of  around  a  corner,  as  in  the  case  where  beams  are 

[220] 


Systems  of  Reinforcement  Employed 

used.     The  method  of  construction  which  he  employs  is  known 
as  the  mushroom  system. 

Merrick  System.— To  lighten  the  weight  of  the  concrete  slab, 
Mr.  Ernest    Merrick   has   designed   a   hollow  floor    construction, 


Concrete 
/  '"   2  parts  sand 


T      .  » 

.:...•:•:•  •••:•:•  :^,::.:---'^::'i'---:---^.---  ••;:•'•>:  *::•.:,•.:•••;•:•.  -..v.^--""-'--"-ij 

•«•     t-let 

illiiii^iiiiH 

1     -7       f: 

iM^MMiiKMM^ 

\ 


f  1  part  portlMd  e 
Concrete  j  2  parts  (and 

(.Hair  «  requirtd 


FIG.  61. 


consisting  of  a  series  of  reinforced  concrete  beams  connected  by  a 
concrete  plate  at  the  top  and  a  ceiling  plate  at  the  bottom. 

Melan  System. — In  the  Melan  system  of  constructing  bridges, 
steel  ribs  or  I-beams  of  considerable  size  are  employed;  the  steel 
carrying  the  major  portion  of  the  stress,  while  the  concrete  serves  as 
protective  covering. 

The  Columbian  System. — This  is  a  flat  concrete  system  with 


TYPICAL    DETAILS 


H 

r  -  " 


L::: 


a_ 


FIG.  62. — The  Gabriel  System  of  Reinforcement. 

ribbed  steel  tension  members.  Rolled  joists  are  used  for  beams, 
embedded  in  concrete,  the  double  cross  floor  reinforcement  being 
held  in  place  by  flat  iron  inverted  stirrups  placed  over  the  top  flanges 
of  the  joists. 

[221] 


Handbook  for  Cement  and  Concrete  Users 

The  Unit  System. — In  the  Unit  System,  which  is 'controlled  by 
the  Unit  Concrete  Steel  Frame  Company  of  Philadelphia,  all  of 
the  metallic  reinforcement  for  each  beam  or  girder  is  made  into  a 
single  unit  and  placed  as  a  unit  in  the  form.  This  is  accomplished 
by  having  both  the  straight  and  camber  bars  fastened  together  by 
stirrups  and  clamps,  so  that  each  tension  and  shear  member  is 
rigidly  held  in  its  proper  position.  This  precludes  the  possibility 
of  one  or  more  members  being  omitted  or  incorrectly  placed  by 
workmen  at  the  building,  and  affords  opportunity  for  inspection 
prior  to  use. 

The  advantages  claimed  for  this  system  are  absolute  accuracy 
in  the  placing  of  the  reinforcing  material;  the  ease  with  which  it  can 
be  inspected  and  errors,  if  any,  detected  and  corrected  before  con- 
creting; the  impossibility  of  omitting  any  tension  or  shear  member; 
the  additional  strength  secured  by  binding  the  slab  concrete  to  the 
beam  concrete  by  means  of  lacing  of  the  slab  reinforcement  through 
the  stirrups.  The  girder  frames  may  thus  be  set  in  advance  of  the 
concrete  workj  and  provision  made  for  shafting  or  other  overhead 
fixtures. 


[222] 


CHAPTER  XX 

REINFORCED    CONCRETE    IN    FACTORY   AND 
GENERAL    BUILDING   CONSTRUCTION 

Advantages  of  Reinforced  Concrete  in  Building  Construction. — Practical  Details  of 
Construction.  Slabs,  Columns,  Floors,  Loads,  Walls. — Roofs. — Attaching  Ma- 
chinery. 

IN  the  factory,  where  the  primal  considerations  are  serviceability, 
fireproofness,  and  cost,  concrete  has  found  one  of  its  leading  appli- 
cations. When  reinforced  with  steel,  a  structure  is  obtained  which  is 
lower  in  first  cost  than  an  all-steel  building,  which  can  be  more 
quickly  erected,  and  which  is  freer  from  vibration  and  more  fire- 
proof. 

As  compared  with  what  is  known  as  the  "  slow-burning,"  or 
"mill"  type  of  construction,  reinforced  concrete  is  more  fireproof, 
durable,  and  carries  a  lower  rate  of  insurance  as  the  mill  type  is  a 
combination  of  brick,  stone,  or  concrete  walls  with  timber  floors  and 
columns. 

Cost. — While  all  statements  as  to  cost  of  reinforced  concrete 
buildings  may  be  somewhat  unreliable,  it  is  safe  to  figure  that  in 
the  simple  factory  building  where  elaborate  forms  are  not  required 
and  building  material  prices  not  excessive,  the  cost  will  be  about 
8  cents  per  cu.  foot.  This  price  will  increase  with  elaboration  of 
surface  finish  and  ornamentation  and  other  unfavorable  conditions 
to  12  cents  per  cubic  foot. 

The  volume  includes  the  building  from  footing  to  roof  and  the 
price  does  not  include  interior  work  such  as  lighting  or  heating 
plants,  machinery,  plastering,  plumbing,  or  elevators. 

Fire  resistance  is  one  of  the  chief  inducements  that  has  led  to 
the  extensive  use  of  concrete  in  factories.  The  materials  to  be 
employed  are  first-class  Portland  cement,  quartz  sand,  and  broken 
trap  rock.  Limestone  aggregates  are  more  easily  injured  by  ex- 
treme heat  and  gravel  is  more  readily  dislodged.  Cinders  make  a 

[223] 


Handbook  for  Cement  and  Concrete  Users 

good  aggregate  for  fire  resistance,  but  the  concrete  made  therefrom 
is  not  sufficiently  strong  for  reinforced  concrete  work  excepting  for 
partition  walls  and  short  spans. 

A  reinforced  concrete  factory  is  necessarily  a  very  stiff  structure, 
every  part  being  inseparably  connected  with  every  other  part  by 
continuous  beams,  girders,  and  slabs.  This  permits  the  operation 
of  the  heaviest  machinery  with  much  less  vibration  than  equivalent 
steel  structures. 

In  taking  up  the  question  of  a  concrete  factory,  the  layout  and 
arrangement  of  machinery  should  first  be  made  and  the  building 
designed  to  accommodate  the  resulting  loads. 

One  of  the  distinct  advantages  of  a  concrete  factory  is  the  large 
amount  of  window  space  and  light  thus  made  available  which  is 
due  to  the  inherent  strength  of  concrete  and  the  thin  members 
required  to  support  the  windows,  etc.  In  addition  to  these  ad- 
vantages the  floors  of  concrete  may  be  made  absolutely  watertight, 
can  readily  be  flushed  with  a  hose,  and  are  fire-  and  vermin-proof. 

Practical  Construction  Details. — The  essential  principles  govern- 
ing the  design  of  girders,  columns,  and  slabs,  have  already  been  given 
in  Chapters  XVII  and  XVIII.  The  following  data  is  of  importance 
in  connection  with  building  and  factory  construction,  and  is  taken 
from  "Reinforced  Concrete  in  Factory  Construction,"  by  Sanford 
E.  Thompson.* 

Floor  Slabs. — The  thickness  and  reinforcement  of  the  floor 
slabs  are  determined  by  the  distance  between  the  beams,  and  by  the 
loading  which  will  come  upon  them.  The  most  usual  thicknesses  are 
31/2  inches  to  5  inches,  with  reinforcement  calculated  from  the 
bending  moment  produced  by  the  loads.  An  economical  quantity 
of  steel  is  apt  to  be  from  0.8  per  cent  to  i  per  cent  of  the  sectional 
area  of  the  slab  above  the  steel. 

A  few  rods  are  usually  placed  at  right  angles  to  the  main  bearing 
rods  of  the  slab  to  assist  in  preventing  contraction  cracks,  and  these 
also  add  to  the  strength  of  the  slab. 

In  a  factory  or  warehouse  the  most  economical  floor  surface  is 
generally  a  granolithic  finish,  consisting  of  a  layer  of  i :  2  mortar 
about  three-quarter  inch  thick,  spread  upon  the  surface  of  the  con- 

*  Published  by  the  Atlas  Portland  Cement  Co. 
[224] 


Reinforced  Concrete  in  Building  Construction 

crete  slab  before  it  has  begun  to  set,  and  trowelled  to  a  hard  finish 
just  like  a  concrete  sidewalk. 

Machines  are  readily  bolted  to  the  concrete  by  drilling  small  holes 
in  the  concrete  at  the  proper  points  for  the  standards  and  grouting 
the  lag  screws  in  place,  or  else  bolting  them  through  the  slab. 

If  for  any  reason  a  wood  floor  is  required,  stringers  may.  be  laid 
upon  the  top  of  the  concrete  and  spaces  left  between  them  or  filled 
with  cinders  or  with  cinder  concrete. 

Stirrups. — Besides  the  ordinary  compression  and  pull  in  a  beam, 
there  are  secondary  stresses  of  shear  or  diagonal  tension,  which,  if 


FIG.  63.— Ordinary  Type  of  Ribbed  Slab. 

not  provided  for,  will  produce  diagonal  cracks.  These  will  run  in 
a  general  direction  from  the  bottom  of  the  beam  near  the  supports 
on  an  incline  toward  the  top  of  the  beam,  and  may  cause  the  beam 
to  fail.  To  prevent  this  cracking,  unless  the  beam  is  so  wide  that 
the  concrete  can  take  the  whole  of  the  stress  without  exceeding  60 
pounds  per  square  inch  in  shear,  vertical  or  inclined  steel  bars,  of 
sizes  accurately  computed,  must  be  placed.  The  bent-up  tension 
rods  take  care  of  a  part  of  this  shear,  or  diagonal  tension,  but  if 
these  are  not  sufficient,  stirrups,  which  are  usually  made  in  the 
form  of  a  U,  must  be  inserted  at  the  proper  locations  to  take  the 
remainder. 


Handbook  for  Cement  and  Concrete  Users 


Columns. — The  most  important  of  all  the  members  of  the 
building  are  the  columns,  for  if  a  column  fails,  the  entire  building  is 
liable  to  go  down. 

If  columns,  as  ordinarily  built  in  building  construction,  are 
made  of  i :  2 :  4  proportions,  it  is  safe  in  an  ordinary  building  to  allow 
a  direct  compressive  strength  of  450  pounds  per  square  inch,  pro- 
vided the  columns  are  at  least  12  inches  square.  A  customary 
manner  of  designing  is  to  figure  the  entire  compression  upon  the 
concrete  to  the  full  size  of  the  column,  but  to  place  four  or  possibly 
six  rods  of  5/8  inch  or  3/4  inch  diameter  near  the  corners  or  sides  of 


FIG.  64. — Column  Reinforcement. 


FIG.  65. — Reinforced  Concrete 
Column  Footing. 


the  column,  with  i/ 4-inch  wire  loops  around  these  rods  at  occasional 
intervals  in  the  height,  say,  from  8  to  1 2  inches  apart. 

Vertical  steel  rods  of  larger  size  may  be  introduced  when  it  is 
necessary  to  decrease  the  size  of  the  columns.  These  may  be  com- 
puted to  bear  a  portion  of  the  compressive  load,  but  they  cannot  be 
figured  at  their  full  safe  value  of  16,000  pounds  per  square  inch 
because  they  have  a  different  modulus  of  elasticity  and  compressive 
strength  from  concrete  and  can  only  shorten  the  same  amount  as  the 
concrete.  Under  ordinary  circumstances,  therefore,  they  cannot  be 
assumed  to  bear  more  than  the  safe  compressive  stress  in  the  con- 
crete times  the  ratio  of  elasticity  of  steel  to  concrete,  or  about  7,000 
pounds  per  square  inch.  Because  of  this  small  amount  of  compres- 

[226] 


Reinforced  Concrete  in  Building  Construction 

sion  which  they  can  bear,  it  is  always  cheaper  to  enlarge  the  column 
rather  than  to  insert  steel  of  large  diameter  to  assist  in  taking  the 
load. 

Another  means  of  increasing  the  strength  of  the  column  is  to 
use  a  richer  mixture.  This  is  legitimate  provided  the  same  mixture 
is  carried  up  through  the  floor  system  at  the  column  so  that  there 
will  be  no  weak  places.  By  using  proportions  i :  i :  3,  a  safe  working 
compression  in  the  concrete  of  700  pounds  per  square  inch  may  be 
adopted. 

Hooped  columns,  that  is,  columns  reinforced  with  bands 
placed  near  together  or  with  spirals,  are  frequently  adopted 
to  reduce  the  size  of  the  column.  It  is  a  serious  question  in 
the  minds  of  conservative  engineers  as  to  whether  it  is  good 
practice  to  assume  that  a  large  proportion  of  the  load  can  be  borne 
by  such  hoops.  Although  tests  have  shown  that  hooped  columns 
have  a  high  ultimate  strength,  these  same  tests  prove  that  the  con- 
crete within  the  hoops  is  overstrained  before  the  hoops  begin  to 
take  any  of  the  tension  which  must  reach  them  before  they  can 
strengthen  the  columns. 

Basement  Floor. — The  earth  under  a  basement  floor  must  be 
well  drained.  If  necessary,  drains  of  tile  pipe  or  of  screened  gravel 
or  stone  may  be  placed  in  trenches  just  below  the  concrete,  or  the 
entire  level  may  be  covered  with  cinders  or  stone.  If  the  basement 
is  below  tide  water  or  ground  water  level,  it  is  not  safe  to  depend 
upon  the  concrete  itself  being  water-tight,  and  waterproofing 
should  be  provided  for  as  described  in  Chapter  XXX. 

For  a  basement  floor  in  dry  ground  a  3-inch  or  4-inch  thickness  of 
ordinary  1:3:5  concrete, — that  is,  concrete  composed  of  i  part  Port- 
land cement  to  3  parts -sand  to  5  parts  broken  stone  or  gravel — may 
be  laid  and  the  surface  screeded  to  bring  it  to  the  required  level.  As 
it  sets,  this  concrete  should  be  trowelled  just  as  the  wearing  surface 
of  a  sidewalk  is  trowelled,  but  without  the  mortar  or  granolithic 
finish  which  is  customarily  laid  upon  a  walk.  If  the  floor  is  to 
have  a  great  deal  of  wear  or  trucking,  the  usual  3/4-inch  or  i-inch 
layer  of  i :  2  mortar  may  be  laid  upon  the  concrete  before  it  has  set, 
forming  a  part  of  the  total  thickness  of  4  inches;  but  usually  this 
is  an  unwarranted  expense  in  a  basement,  as  the  plain  concrete  will 
give  as  good  service. 

[227] 


Handbook  for  Cement  and  Concrete  Users 

It  is  well  in  any  case  to  divide  the  floor  into  blocks,  say,  8  or 
10  feet  square,  so  that  any  shrinkage  cracks  will  come  in  the  joints. 
This  is  readily  accomplished  by  laying  alternate  blocks,  and  then 
filling  in  the  intermediate  ones  the  next  day. 

Design  of  Floor  System. — Loading. — In  designing  a  rein- 
forced concrete  building,  the  first  consideration  is  the  loading 
which  the  various  floors  must  sustain;  in  other  words,  the 
strength  which  each  floor  must  have  to  support  the  weights 
which  may  come  upon  it  under  all  conceivable  conditions.  In 
a  factory  or  warehouse  it  is  frequently  possible  to  accurately  cal- 
culate the  maximum  weight  which  will  come  upon  a  given  area 
of  floor.  For  the  very  heaviest  loading  the  problem  is  frequently 
the  simplest,  since  the  heavy  weights  are  apt  to  be  due  to  the 
storage  of  merchandise  whose  weight  per  cubic  foot,  and  there- 
fore per  square  foot  of  floor,  can  be  readily  calculated.  Some- 
times the  underside  of  the  floor  must  support  tracks  which 
carry  certain  definite  weights,  and  the  beams  or  girders  must  be 
calculated  for  these  concentrated  loads  in  addition  to  the  uniform 
loads  upon  the  floor. 

In  computing  the  strength  of  the  floor  system,  the  weight  of  the 
concrete  itself  must  always  be  allowed  for.  In  very  long  spans 
the  concrete  frequently  weighs  more  than  the  load  which  will  be 
placed  upon  it. 

In  many  cases  the  loading  must  be  assumed  without  actual 
computation.  A  maximum  load  must  frequently  be  selected  to 
support  machinery  whose  weight  is  slight  but  whose  vibrations 
,  require  a  stiff  floor  system. 

The  various  conditions  met  with  in  warehouse  or  factory  con- 
struction may  thus  necessitate  loadings  varying  from  100  to  500 
pounds  per  square  foot  of  floor  area,  very  wide  limits  and  yet  not 
more  than  occur  in  practice. 

As  a  guide  to  the  selection  of  floor  loads,  the  following  values 
are  suggested: 

Office  floors 100  pounds  per  square  foot 

Light -running  machinery 150  pounds  per  square  foot 

Medium  heavy  machinery 200  pounds  per  square  foot 

Heavy  machinery 250  pounds  per  square  foot 

Storage  of  parts  or  finished  products,  depending 

upon  actual  calculated  loads 150  to  500  pounds  per  square  foot 


Reinforced  Concrete  in  Building  Construction 


When  the  loads  are  apt  to  occur  only  over  a  part  of  the  floor,  the 
slabs  and  beams  are  calculated  for  the  full  load,  and  when  com- 
puting the  girders  and  columns  a  slightly  smaller  load  is  sometimes 
used.  For  example,  if  the  slabs  and  beams  are  figured  for  200 
pounds  per  square  foot  of  floor  area,  it  might  be  assumed  that  the 
whole  of  the  total  area  supported  by  a  girder  or  column  would 
never  be  loaded  at  once,  and  the  load  per  square  foot  actually  reach- 

TABLE  XXI. — ALLOWABLE  FLOOR  LOADS  IN  ACCORDANCE  WITH 
THE  BUILDING  LAWS  OF  VARIOUS  CITIES. 

(From  Kahn's  Pocketbook.) 


Live  Loads  for  Floors  in  Different  Classes  of  Build- 
ings Exclusive  of  the  Weight  of  the  Materials  of 
Construction. 

New  York 
1902. 

Chicago 
1902 

Philadelphia 
1902. 

li 

San 

Francisco 
1906. 

Pounds  per  Square  Foot. 

Dwellings,    Apartment   Houses,    Hotels,     Tene- 
ment Houses  or  Lodging  Houses 

60 

75 
75 

75 
90 

120 

5° 
30  ' 
300 

40 

100 
100 

40* 

100 
100 

25 

25 

70 

100 
100 

120 
120 
15°    ' 

3° 
3° 

So 

100 
100 

80 
150 

250 

25t 
25t 

15° 

60 

150 

75 
75 

75 
125 

120 
250 

5° 
3° 
300 

Office  Buildings,  ist  Floor  

Office  Buildings  Above  ist  Floor  .          . 

Schools  or  Places  of  Instruction  

Stables  or  Carriage  Houses 

Buildings  for  Public  Assembly 

Buildings  for  Ordinary  Stores,  Light  Manufactur- 
ing and  Light  Storage           . 

Stores  for  Heavy  Materials,  Warehouses,    and 
Factories  ..    .        

Roofs  —  Pitch  less  than  20  degrees  .            .        . 

Sidewalks       

Public  Buildings  Except  Schools 

ing  the  girder  and  column  at  any  one  time  would  be  therefore  not 
more  than  1 50  pounds  per  square  foot  of  floor  area. 

Layout. — The  general  layout  of  the  beams  and  girders  and 
columns  depends  upon  the  loading,  the  uses  to  which  the  building 
is  to  be  put,  and  the  ground  area.  Frequently  in  a  large  building, 

*  Stables  less  than  500  square  feet  in  area. 

f  Stables  over  500  square  feet  in  area. 

J  Make  proper  allowance  for  wind  at  30  Ibs.  per  square  foot  horizontal  pressure. 

[2291 


Handbook  for  Cement  and  Concrete  Users 

it  will  be  worth  while  to  require  the  engineer  to  make  several  com- 
parative estimates  with  different  spacings  of  columns  and  sizes  of 
panels,  so  as  to  determine  that  which  is  most  economical  consistent 
with  the  floor  area  required  for  the  machinery. 

Common  spacings  of  columns  in  a  reinforced  concrete  building 
are  from  12  feet  to  20  feet.     Longer  spans  are  not  usually  so  eco-4 
nomical,  but  may  frequently  be  necessary  to  give  the  floor  space 
required  for  machinery  or  storage. 

Walls. — The  walls  of  reinforced  concrete  factories  are  sometimes 
built  up  with  the  columns,  but  it  is  generally  considered  more 
economical  to  erect  the  skeleton  structure  and  fill  in  the  wall  panels 
afterwards. 

Slots  in  the  columns  are  made  by  nailing  a  strip  on  the  inside  of 
the  column  forms.  In  this  way  the  panels  are  mortised  into  the 
columns. 

Ordinary  concrete  walls  require  light  reinforcement  to  prevent 
shrinkage  and  give  them  stiffness  while  setting.  All  that  is  required 
for,  say  a  4-inch  or  6-inch  wall,  are  i/  4-inch  rods  spaced  from  12 
to  24  inches  apart,  according  to  the  size  and  importance  of  the  wall. 
At  window  and  door  openings  a  larger  amount  of  reinforcement  is, 
of  course,  necessary,  and  in  these  cases  the  amount  of  steel  must  be 
calculated  just  as  though  the  lintels  were  reinforced  concrete 
beams. 

Roofs. — Reinforced  concrete  roofs  are  designed  like  floors.  A 
roof  load  commonly  assumed  in  temperate  climates,  to  provide  for 
roof  covering,  snow  and  wind  pressure,  is  40  pounds  per  square 
foot,  in  addition  to  the  weight  of  the  concrete  itself. 

It  is  not  safe  to  assume  that  the  concrete  roof  of  itself  will  be 
water-tight  unless  special  provision  is  made  in  the  construction. 
Although  tanks  and  walls  can  readily  be  made  to  hold  water,  a  roof 
is  under  extraordinarily  disadvantageous  conditions  because  of  the 
rays  of  the  sun.  Usually,  therefore,  a  tar  and  gravel  or  other  form 
of  roof  covering  must  be  provided. 

Methods  for  Attaching  Shafting,  etc. — The  attachment  of 
shafting,  piping,  etc.,  to  the  ceilings  of  reinforced  concrete  buildings 
presents  no  special  difficulty,  provided  adequate  provision  is  made 
in  the  design. 

The  following  methods  are  employed : 

[230] 


Reinforced  Concrete  in  Building  Construction 


i.  Bolts  are  embedded  in  the  concrete  beams  with  their  threaded 
ends  hanging  down.  After  the  forms  have  been  removed  timbers 
are  bolted  to  the  undersides  of  the  beams  and  the  hangers  for  the 


FIG.  66. 


WoodSMp 
ffpg/t 


'es 


FIG.  67. 


toy  scnwfr  /o  4*f 


^fe?^;W.^^pl 


&&'tfmm 

jy/s/v/v.  — -*j    j 


fit  MHO*  \\  fia 

@  before  /"/>  fo//e<f 


FIG.  68. 
FIGS.  66,  67,  68.  —  Showing  Method  of  Supporting  Shafting  from  Concrete  Ceiling. 

shafting  are  attached  to  the  timbers  in  the  usual  way  by  means  of 
lag  screws. 

2.  Sockets  into  which  a  bolt  can  be  threaded  are  fastened  to  the 
reinforcing  bars.     Such  sockets  also  serve  as  spacers  for  the  bars. 

3.  Sockets  into  which  a  bolt  can  be  threaded  are  suspended  by 
stirrups,  embedded  in  the  beam. 


Handbook  for  Cement  and  Concrete  Users 

The  suspended  bolts  in  methods  1-3  are  used  to  fasten  either 
a  timber  or  a  steel  channel  or  other  shape  to  the  bottom  of  the 
girder,  from  which  the  hangers  or  piping  are  supported. 

4.  A  slotted  pipe  is  suspended  by  stirrups  and  used  for  attaching 
the  hangers  or  other  fittings  directly  to  the  concrete  without  the 
interposition  of  a  timber  or  metal  beam.     The  attachment  is  made 
by  means  of  T-bolts  which  are  suspended  from  the  pipe,  and  pass 
through  the  bolt-holes  in  the  hangers. 

5.  Instead  of  a  slotted  pipe,  two  angles  are  fastened  to  a  wooden 
strip  and  suspended  from  the  bottom  of  the  beam  by  anchor  bolts, 
the  angles  being  separated  so  as  to  form  a  slot,  from  which  T-bolts 
can  be  suspended  at  any  point  as  in  4. 

6.  A  horizontal  hole  is  drilled  in  the  top  of  the  beam,  and  a  bolt 
inserted.    From  this  a  vertical  rod  is  hung. 


CHAPTER  XXI 

CONCRETE    IN    FOUNDATION    WORK 

Importance  of  Foundations. — Loads  on  Foundations. — Methods  of  Securing  Good 
Foundations. — Essential  Requirements  in  Construction. — Concrete  in  Foundations. 
— Reinforced  Concrete  Piles. — Caissons. — Cribs. 

Importance  of  Foundations. — Every  structure  must  depend  for 
its  security  upon  the  integrity  of  its  foundation  and  whatever  its 
character,  if  the  main  prop  be  weakened,  the  edifice  it  supports  is 
bound  to  suffer  or  fail.  The  importance  of  securing  firm  and 
stable  foundations  has  brought  to  the  study  of  the  subject  the  ablest 
constructive  brains  of  the  engineering  world  and  the  difficulties 
which  engineering  genius  have  overcome  has  rendered  possible  the 
monumental  engineering  structures  of  to-day.  While  there  is  no 
difficulty  in  rearing  obelisks  on  extensive  areas  of  firm  earth  or  rock 
beds  as  has  been  cjone  in  ancient  days,  the  placing  of  enormous 
skyscrapers,  bridge  piers,  carrying  thousands  of  tons  of  weight,  and 
other  gigantic  structures  upon  soft  and  shifting  beds,  or  in  water 
and  quicksand,  is  a  distinct  modern  development,  and  concrete  has 
played  no  small  part  in  this  development. 

Reference  to  the  foundations  of  various  structures  such  as  walls, 
arches,  sidewalks,  sewers,  etc.,  will  be  found  in  the  appropriate 
chapters,  and  it  is  intended  here  to  outline  the  general  principles 
common  to  all  foundations,  as  well  as  to  describe  the  different  types 
that  are  referred  to. 

The  basic  principles  lying  at  the  root  of  all  foundation  problems 
are: 

1.  That  the  bed  upon  which  the  structure  rests,  i.e.,  the  founda- 
tion bed,  must  not  be  compressed  beyond  certain  limits  which 
experience  has  established  as  those  which  they  can  safely  stand. 

2.  That  the  material  composing  the  foundation  bed  be  sufficiently 
stable  so  as  to  prevent  any  displacement  or  tendency  to  displacement. 

Safe  Loads  on  Foundations. — The  order  of  desirability  in  which 
various  foundation  beds  arrange  themselves,  and  the  amount  of 

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Handbook  for  Cement  and  Concrete  Users 

unit  pressure  each  can  safely  bear  as  determined  by  tests  and  ex- 
perience, are  as  follows: 

ALLOWABLE  PRESSURES  ON  FOUNDATIONS. 

Rock 10  to  50  tons  per  square  foot. 

Hardpan 8  "      "        " 

Sand 4  "       " 

Clay 1-3          "      " 

Muck  o-i  "      "        " 

Concrete    10 

Methods  of  Securing  Good  Foundations  in  Poor  Soils. — The 

construction  of  foundations  in  ordinary  soil  where  the  load  to  be 
carried  does  not  exceed  the  safe  bearing  value  of  the  material  is  a 
simple  matter;  but  when  a  very  heavy  load  is  to  be  placed  on  a 
poor  soil,  various  methods,  depending  upon  local  conditions,  must 
be  employed  to  distribute  the  load  upon  a  sufficiently  wide  area  of 
foundation  bed  so  that  the  pressure  per  square  foot  will  be  within 
safe  limits.  This  may  be  done  by: 

1.  Spreading  the  foundation  over  a  sufficient  area  by  means  of 
footings  or  grillages. 

2.  Carrying  the  structure  on  wooden  or  concrete  piles,  piers, 
caissons,  or  cribs. 

3.  Consolidating   and    confining   the   materials  in  the  founda- 
tion bed    so  as   to    increase   its   bearing   power.      This   may   be 
effected   in  several  ways   and   is   particularly  useful   when   quick- 
sand is  encountered.      In  such  cases,  grout  may  be  poured  into 
the   material  which   will   set   up   and   produce   a  rock-like  mass; 
holes  may  be  bored  and  filled  with   sand,  or   piles   may  be  em- 
ployed.     During  construction,  quicksand  is  sometimes  frozen  by 
what  is  known  as  the  Poetch  Freezing    Process   and    excavation 
carried  on  in  frozen  material. 

Soft  materials  in  foundation  beds  may  be  confined  by  the  con- 
struction of  a  timber  or  steel  cofferdam  or  box  around  the  area  to  be 
confined. 

Essential  Requirements  in  Construction. — In  the  construction 
of  all  ordinary  foundations,  on  earth  or  rock  beds,  a  few  essential 
requirements  may  be  pointed  out. 

i.  The  foundation  should  in  all  cases  be  below  the  frost  line  at 
the  locality  in  question. 


Concrete  in  Foundation  Work 

2.  Poor  material  such  as  vegetable  or  decayed  matter,  dis- 
integrated rock,  etc.,  should  be  removed  and  replaced  by  good 
sand,  earth,  or  concrete. 

3.  Adequate  drainage  should  be  secured  so  as  to  remove  danger 
of  washing  out  of  soil.     Springs  encountered  in  foundation  sites 
must  be  stopped  up  by  grouting  or  carried  off  in  pipes. 

4.  Where  walls  and  similar  structures  are  to  rest  on  sloping 
beds,  the  latter  should  be  stepped  to  prevent  any  tendency  of  the 
superstructure  to  slide. 

5.  The  loads  placed  on  the  foundation  bed  should  be  uniform 
over  all  parts  of  the  area,  as  unequal  loading  will  lead  to  unequal 
compression  of  the   underlying  material  and   result  in  unequal 
settlement.     Evidence  of  the  disregard  of  this  requirement  is  visible 
in  settlement  cracks  which  may  frequently  be  seen  in  new  structures 
within  a  short  time  after  their  erection. 

Concrete  for  Foundations. — Concrete,  either  plain  or  reinforced, 
is  in  all  probability  the  most  satisfactory  material  for  foundation 
work  that  has  yet  been  found.  Being  in  a  plastic  state  when  laid, 
it  easily  fills  all  irregularities  in  the  foundation  bed  and  insures  an 
even  and  equal  bearing  throughout.  Concrete  for  foundations  can 
be  placed  under  water  almost  as  readily  as  in  air.  Practically  the 
only  precautions  necessary  are  to  see  that  the  water  is  at  rest,  and  in 
placing  the  concrete,  to  do  so  with  as  little  fall  as  possible  through 
the  water,  so  as  to  prevent  washing  out  the  cement. 

Concrete  unreinforced  has,  until  quite  recently,  been  used  for 
all  classes  of  foundation  work,  but  the  tendency  at  the  present  time 
in  many  cases  is  to  substitute  reinforced  concrete.  Owing  to  the 
low  tensile  resistance  of  plain  concrete,  the  thickness  is  proportion- 
ately great,  thus  requiring  a  large  amount  of  material  and  greatly 
increasing  the  amount  of  excavation  necessary.  In  using  rein- 
forced concrete  the  thickness  may  be  greatly  diminished  and  a 
large  saving  in  cost  effected. 

Concrete  Footings.— Figs.  69,  70,  71  represent  the  same  footing 
designed  first  in  ordinary  concrete,  second  using  a  steel  grillage; 
third,  in  reinforced  concrete. 

This  footing  is  designed  to  carry  a  load  of  400,000  Ibs. ;  bearing 
capacity  of  the  soil,  6,000  Ibs.,  per  square  foot. 

The  economy  of  the  reinforced-concrete  footing,  both  as  regards 

l*3S] 


Handbook  for  Cement  and  Concrete  Users 

material  and  excavation,  is  at  once  apparent.  The  plain  concrete 
footing  (Fig.  69),  requires  215  cu.  ft.  of  concrete.  The  steel 
grillage  footing  (Fig.  70),  requires  137  cu.  ft.  of  concrete  and  about 
5,000  Ibs.  of  structural  steel.  The  reinforced-concrete  footing 
(Fig.  71),  requires  136  cu.  ft.  of  concrete  and  less  than  600  Ibs.  of 


FIG.  69.  —  Plain  Concrete  Column 
Footing. 


FIG.  70.  —  Concrete  and  Steel  Grillage 
Column  Footing. 


steel.     When  excavation  is  taken  into  account  a  still  greater  economy 
is  shown  in  favor  of  reinforced  concrete. 

Instead  of  a  simple  isolated  footing,  a  combined  footing  support- 
ing two  or  more  columns  at  the  same  time  may  be  necessary.     Here 


FIG.  71. — Reinforced-Concrete  Column  Footing. 

again  reinforced  concrete  proves  more  economical  than  inverted 
concrete  arches  or  steel  grillage. 

Fig.  70  gives  a  longitudinal  section  and  a  cross-section  of  a 
combined  reinforced-concrete  footing.  Some  designers  make  the 
footing  the  same  width  from  bottom  to  top  as  indicated  by  the 

[236] 


Concrete  in  Foundation  Work 

dotted  lines  in  the  cross-section,  in  which  case  the  amount  of  concrete 
is  increased,  but  the  cost  of  form  work  is  decreased  somewhat.  Also, 
in  the  latter  case  no  additional  reinforcement  will  be  necessary  for 
shear,  while  some,  in  the  form  of  stirrups  may  be  necessary  in  the 
former. 

A  further  development  of  the  combined  footing  is  the  raft  footing. 
In  this  case  there  are  more  columns,  or  a  whole  building  may  be 
supported  on  one  footing.  The  footing  acts  as  an  inverted  floor 

5.  :J 


........  •/•  ........... 


FIG.  72.    Combined  Reinforced-Concrete  Column  Footing. 

carrying   the   upward  pressure  of  the  soil  to  the  columns  and  is 
designed  as  such. 

Where  the  foregoing  types  of  foundations  fail  to  develop  suffi- 
cient resistance  to  support  the  loads  upon  them  some  other  form  of 
foundation  must  be  used,  such  as  piles  or  caissons. 

REINFORCED  CONCRETE  PILES 

Historical. — The  first  concrete  piles  were  made  in  France  by 
Mr.  F.  Hennebique,  in  1896.  These  piles  were  cast  in  a  convenient 
location  and  driven  with  a  pile-driver  the  same  as  an  ordinary  wood 
pile.  About  the  same  time,  A.  Raymond  of  Chicago,  conceived  the 
idea  of  a  pile  cast  in  place.  The  Simplex  pile  which  was  patented 
in  1903,  is  also  a  cast-in-place  pile,  although  the  method  of  casting 
is  different  than  in  the  Raymond  pile.  Since  the  introduction  of 
the  above  pile,  various  other  piles  have  been  developed,  but  are 
really  little  more  than  modifications  of  the  Hennebique,  Raymond, 
and  Simplex  piles. 

Advantages. — An  ordinary  wood  pile  will  carry  a  load  of  about 
15  tons;  a  reinforced-concrete  pile  may  be  loaded  with  thirty  to 
fifty  tons,  depending  on  the  nature  of  the  ground.  Wood  piles, 
unless  continually  saturated  with  water  are  subject  to  rapid  decay, 

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Handbook  for  Cement  and  Concrete  Users 

and  even  when  under  water  are  subject  to  the  attack  of  wood-borers. 
Reinforced-concrete  piles  are  not  subject  to  decay  or  to  the  attack 
of  any  destructive  animal  life.  Reinforced-concrete  piles  may, 
therefore,  be  used  where  a  wood  pile  would  not  be  advisable.  A 
concrete  pile  may  have  the  lower  end  continually  submerged,  its 
middle  portion  alternately  wet  and  dry,  and  the  top  portion  always 


•sapr 


FIG.  73. — Comparative    Sections.      Wooden    and    Corrugated    Reinforced-Concrete 

Pile   Foundations. 


dry,  without  being  in  any  way  harmful  to  the  pile,  or  in  any  way 
shortening  its  life.  A  timber  pile  under  similar  conditions  would 
last  but  a  very  short  time. 

Disadvantages. — The  argument  most  frequently  used  against 
reinforced-concrete  piles  is  their  cost.  While  the  cost  per  linear 
foot  of  a  reinforced-concrete  pile  is  certainly  greater  than  that  of  a 

[238] 


Concrete  in  Foundation  Work 

wood  pile,  still  when  the  much  greater  bearing  power  of  the  rein- 
forced-concrete  pile  is  considered  the  additional  cost  per  linear  foot 
is  discounted;  in  fact,  the  reinforced-concrete  pile  is  likely  to  prove 
the  more  economical. 

Types  of  Piles. — Reinforced-concrete  piles  may  be  divided  into 
two  classes.  First,  the  cast-and-driven  pile;  second,  cast-in-place 
pile. 

The  Cast-and- Driven  Pile. — Piles  of  this  type  are  first  cast  in 
some  convenient  locality,  and  when  thoroughly  seasoned  are  trans- 
ported to  the  desired  site  and  driven.  Piles  of  this  type  are  always 
reinforced  both  with  longitudinal  rods  and  hooping.  Great  care  is 
required  in  handling  and  driving  these  piles.  A  cap,  to  take  up  the 
shock  of  the  hammer  and  prevent  shattering  of  the  head  of  the  pile, 


FIG.  74.— The  Chenoweth  Concrete  Pile. 

is  always  used,  and  it  is  on  some  detail  of  this  cap  that  the  patent 
for  the  pile  is  usually  based.  In  general,  the  cap  will  consist  of  a 
cushion  of  confined  sand,  rope,  or  rubber  hose,  upon  which  rests  a 
false  pile.  This  false  pile  receives  the  shock  of  the  hammer,  the 
shock  being  distributed,  by  the  sand,  uniformly  over  the  head 
of  the  pile.  Piles  of  this  type  are  frequently  driven  by  means 
of  a  water  jet,  and  this  is  advisable  for  all  but  short  piles.  It  is 
also  advisable  to  fit  the  pile  with  a  metal  point  so  as  to  facilitate 
penetration. 

The  principal  cast-and-driven  piles  are  the  Hennebique,  Gilbreth, 
Chenoweth,  and  Williams. 

The  " Hennebique"  was  the  first  cast-and-driven  pile.  It  is 
either  rectangular,  triangular,  or  circular  in  cross-sections,  reinforced 
and  driven  as  above. 

[239] 


Handbook  for  Cement  and  Concrete  Users 


In  the  "Gilbreth"  pile  the  cross-section  is  an  octagon  with 
corrugated  side.  The  object  of  the  corrugation  is  to  allow  an  outlet 
for  the  water  from  the  water  jet,  and  to  increase  the  skin  friction. 

The  "Chenoweth"  pile  is  round  and  is  made  without  forms  by 
a  special  machine.  It  is  reinforced  with  a  coiled  sheet  of  wire 
netting  and  longitudinal  steel  rods  placed  near 
the  surface,  at  equal  distances  apart.  The  ap- 
paratus for  rolling  the  pile  consists  of  a  trav- 
elling platform  and  a  roller  between  which  the 
pile  is  formed.  In  operation  the  steel  wire  net- 
ting, with  the  longitudinal  rods  attached,  is 
rfe  K^  spread  on  the  platform  and  covered  with  a  layer 
of  concrete.  One  edge  of  the  netting  is  attached 
to  the  edge  of  the  platform  and  the  other  to 

the    winding    pipe 


or  mandrel.  The 
mandrel  is  then  ro- 
tated and  the  net- 
ting and  its  covering 
of  concrete  is  wound 
or  coiled  up.  At 
the  same  time  and 
as  fast  as  the  net- 
ting and  concrete 
are  coiled,  the  plat- 
form moves  under 
the  roll  and  the  roll 
itself  rotates,  thus 
pressing  the  pile 

mt°  SnaP6'  ^ 

The  "  Williams" 

pile  is  reinforced  by 

an  I-beam.  At  the  point,  the  web  is  cut  away  and  the  flanges 
forged  to  a  point.  The  pile  is  further  reinforced  by  hoops  a  short 
distance  apart. 

Piles  Cast  in  Place.— Piles  of  this  type  may  be  divided  again 
into  two  classes  of  which  the  Raymond  and  Simplex  piles  are 
typical. 

[240] 


FlG.   75. — Raymond  Concrete  Pile  Showing    Partly  Col- 
lapsed Core  and  Shell  and  also  Finished   Pile. 


Concrete  in  Foundation  Work 

In  the  "Raymond"  pile,  a  collapsible  core,  the  size  and  shape  of 
the  pile  desired  is  enclosed  in  a  thick,  closely  fitting,  steel  shell, 
and  driven  with  a  pile  driver  in  the  usual  manner.  After  driving, 
the  core  is  withdrawn,  leaving  the  shell  in  the  ground.  This  shell 
is  then  filled  with  concrete  and  should  reinforcement  be  used,  which 
is  seldom  with  this  pile,  it  is  placed  before  the  filling  commences. 
The  shell  of  these  piles  must  be  of  sufficient  strength  to  hold  its 
shape  after  the  withdrawal  of  the  core. 

The  "Simplex"  system  consists  in  driving  an  extra  heavy  iron 
pipe  into  the  ground  with  a  special  point  to  exclude  the  dirt;  when 
this  pipe  is  driven  to  the  proper  bearing,  a  drop-bottom  bucket, 
filled  with  concrete,  is  lowered  to  the  bottom  of  the  pipe  and  dumped. 
The  bucket  is  then  removed,  a  heavy  weight  lowered  into  the  pipe, 
and  the  pipe  raised  nearly  to  the  top  of  the  concrete,  the  weight 
being  repeatedly  dropped  on  the  concrete,  thus  forcing  it  out  of  the 
end  of  the  pipe.  Another  bucket  of  concrete  is  then  placed  in  the 
pipe  and  the  operation  repeated  until  the  pile  is  formed. 

Two  kinds  of  points  are  used,  depending  upon  the  character  of 
soil  through  which  the  pipe  is  driven.  If  in  soft  soil,  a  cast- 
iron  point  closes  the  end  of  the  pipe,  while  in  stiff  clay  a  pair 
of  jaws  are  used.  These  jaws  are  attached  by  hinges  to  the  bottom 
of  the  pipe,  and  automatically  open  to  permit  the  concrete  to  flow 
through  them  as  the  pipe  is  raised.  The  pipes  used  are  extra  heavy 
steel,  banded  where  necessary,  and  are  made  up  in  sections  of  vary- 
ing lengths  to  suit  the  length  of  pile  required. 

Relative  Advantages  and  Disadvantages. — The  chief  objection 
to  the  cast-and-driven  pile  is  that  it  may  possibly  be  injured  in 
driving.  Careful  driving  will,  however,  prevent  this.  The  ad- 
vantages of  piles  of  this  type  are  that  the  piles  may  be  of  any  length, 
and  can  be  thoroughly  inspected  during  manufacture. 

The  chief  objections  to  the  cast-in-place  pile,  where  a  shell  re- 
mains, are:  First,  the  danger  of  the  light  shell  collapsing;  second, 
the  dropping  of  the  concrete  through  such  a  height  may  cause 
separation.  The  first  objection  is  overcome  by  using  sufficiently 
heavy  shells  and  inspecting  with  an  electric  light  before  filling 
begins.  As  the  concrete  is  usually  a  very  wet  mixture  and  depos- 
ited in  very  small  quantities,  the  second  objection  is  more  fancied 
than  real. 

16  [  241  ] 


Handbook  for  Cement  and  Concrete  Users 

The  disadvantage  of  a  cast-in-place  pile  unprotected  by  a  shell 
is  the  impossibility  of  any  sort  of  inspection.  A  wet  soil  may  carry 
off  some  of  the  cement,  and  a  dry  soil  may  absorb  the  water  necessary 
for  the  proper  setting,  in  either  case  resulting  in  a  pile  of  decreased 
efficiency.  The  rough  surface  of  a  pile  of  this  sort  greatly  increases 
its  bearing  capacity. 

Compressed  Pillar. — The  compressed  system,  controlled  by 
the  Hennebique  Co.,  consists  of  making  a  hole  by  dropping  a  two- 
ton  perforator.  In  very  soft  soil,  clay,  cinders,  and  broken  stone 
are  dumped  into  the  hole  from  time  to  time  and  compressed  by  the 


]  - 

-  -      *  '"-N     "  *' 


Pipe  Driven          -,  ,    Pipeanof  Chc*mt>er 

orn*  Washed        Cn«mt>er  Excavated.  rm*. 

«ut, 

FIG.  76.  —  Concrete  Pile  with  Enlarged  End  Showing  Progressive  Stages  in  Driving. 

perforator  against  the  sides  of  the  hole,  thus  forming  an  almost 
water-tight  lining.  The  hole  is  thus  carried  down  a  suitable  depth, 
concrete  is  then  placed  in  it,  and  is  rammed  with  a  drop  tamper. 
This  results  in  a  pillar  of  large  diameter,  in  which  the  concrete  is 
forced  into  the  surrounding  soil,  thus  greatly  increasing  its  bear- 
ing power.  Both  perforator  and  tamper  are  operated  by  a  pile- 
driver. 

When  soft  material  overlies  strata  of  firm  material,  the  com- 
pressed system  is  particularly  advantageous,  as  by  its  means  a 
large  pier,  resting  on  the  firm  soil  and  extending  through  the  soft 
strata,  results. 

[242] 


Concrete  in  Foundation  Work 

Caissons. — Where  all  other  methods  of  securing  a  satisfactory 
foundation  fail,  caissons,  either  open  or  pneumatic,  carried  down 
to  bed  rock  or  hard  pan,  are  used. 

An  open  caisson  is  a  strong,  water-tight,  bottomless  box,  usually 
constructed  of  steel  or  timber.  It  is  sunk  by  excavating  the  material 
inside  of  it,  and  if  necessary  by  adding  additional  weight  at  its  top. 

Open  caissons  of  reinforced  concrete  have  been  used  in  many 
instances,  notably  in  the  Cockle  Creek  Bridge,  New  South  Wales, 
and  in  the  Catskill  Aqueduct,  in  New  York  State. 

In  the  Cockle  Creek  Bridge,  two  open  cylindrical  reinforced 
concrete  caissons  were  driven  through  a  depth  of  36  ft.  of  silt,  sand, 
and  gravel  to  hard  clay.     When  finally  seated  in  this  clay,  they  were 
filled  with  concrete  and  used  as  piers  for  the  bridge. 

In  the  Catskill  Aqueduct,  three  open  reinforced-concrete  caissons 
were  sunk  in  constructing  the  Rondout  Siphon.  These  caissons 
were  sunk  to  rock,  by  excavating,  under  ordinary  air  pressure,  the 
material  within,  and  allowing  the  caissons  to  sink  of  their  own 
weight.  When  the  aqueduct  is  completed  two  of  the  caissons  will 
serve  as  part  of  the  permanent  lining. 

Pneumatic  Caissons. — A  pneumatic  caisson  is  a  strong,  water- 
tight box,  open  at  the  bottom  and  closed  at  the  top.  This  forms 
a  working  or  air  chamber.  Usually  the  sides  of  the  caisson  are 
continued  above  the  top,  thus  forming  a  second  box  closed  at  the 
bottom  but  open  at  the  top.  This  is  called  the  cofferdam.  The 
pier  is  built  within  this  cofferdam  and  on  top  of  the  caisson  as 
the  sinking  progresses.  The  working  chamber  is  supplied  with 
compressed  air  which  serves  the  double  purpose  of  forcing  out  all 
water,  and  supplying  the  men  with  the  necessary  fresh  air. 

Pneumatic  caissons  are  usually  constructed  of  steel  or  timber, 
though  a  few  have  been  made  of  reinforced  concrete. 

Reinforced  concrete  was  recently  used  in  the  construction  of  the 
large  tunnel  caisson  on  the  Jersey  shore  connecting  the  tunnels  of 
the  Hudson  Co.,  crossing  the  Hudson  River. 

Caissons  are  mostly  used  in  constructing  the  foundations  of 
bridges  and  high  buildings.  When  the  work  is  under  water  or 
in  water-bearing  soil,  the  pneumatic  caisson  is  usually  used,  al- 
though at  times  an  open  caisson  and  a  bucket  dredge  are  sub- 
stituted. 

[243] 


Handbook  for  Cement  and  Concrete  Users 

Cribs. — A  crib  is  usually  a  timber  grillage,  which  instead  of 
being  built  in  place,  is  first  constructed,  then  floated  to  its  final 
resting-place  and  sunk  in  a  single  mass.  The  superstructure  is  then 
built  on  the  crib,  either  in  the  open  or  in  a  caisson,  and  the  function 
of  this  crib  is  to  distribute  the  load  carried  by  the  superstructure  over 
the  foundation  bed. 

While  cribs  are  usually  constructed  of  timber  there  is  no  reason 
why  reinforced  concrete  could  not  be  used  with  economy. 


[244] 


CHAPTER  XXII 

CONCRETE   RETAINING    WALLS,   ABUTMENTS,   AND 

BULKHEADS 

Design  of  Walls  in  General. — Methods  of  Failure.— Kinds  of  Retaining  Walls. — Design 
of  Gravity  Walls. — Reinforced-Concrete  Walls. — Details  of  Construction. — 
Foundations. — Abutments. — Bulkheads. — Appearance  of  Walls. — Tables  for  De- 
sign of  Walls. 

UNTIL  the  advent  of  concrete,  retaining  walls  for  the  support  of 
embankments  and  cuts  as  well  as  reservoir  walls,  bulkheads,  etc., 
were  constructed  of  rubble  or  ashlar  masonry  laid  with  or  without 
mortar  as  the  importance  of  the  problem  demanded.  Concrete, 
especially  when  reinforced,  has  supplied  a  material  which  gives  a 
far  greater  power  of  resistance,  occupies  a  minimum  of  space  and 
may  be  built  at  a  much  lower  cost. 

The  design  of  concrete  retaining  walls  follows  the  same  general 
methods  that  are  employed  for  ordinary  masonry,  the  design  being 
based  upon  the  action  of  the  wall  when  the  load  caused  by  earth, 
water,  or  other  material  from  behind,  comes  upon  it.  Certain 
conditions  of  failure  deduced  from  observation,  experience,  and 
mathematical  reasoning  are  assumed  to  be  possible  and  the  wall  so 
proportioned  that  it  will  be  safe  against  any  and  all  such  possible 
failures.  Thus  it  is- assumed  that: 

Assumptions  Made  in  Design. — A  wall  holding  up  a  bank  of 
earth,  or  water  will  be  subjected  to  a  pressure:  the  amount  of 
which  will  depend  upon  the  depth  of  the  wall  below  the  surface  and 
upon  the  weight  and  mobility  of  the  material  pressing  against  it. 

The  question  as  to  how  much  pressure  is  produced  by  banks  of 
earth  resting  against  walls  has  given  rise  to  much  discussion,  and 
even  to-day  there  is  no  general  agreement  among  engineers  as  to 
what  this  pressure  is.  The  difficulty  arises  from  the  fact  that 
earths  vary  so  much,  their  weight,  consistency,  and  cohesive  power 
are  so  constantly  changing  with  change  of  the  contained  water,  that 
no  general  pressure  rule  can  be  applied.  It  is  thus  that  most  com- 

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putations  for  earth  pressure  assume  a  theoretical  condition,  that  of 
perfectly  dry  sand,  and  yet  this  condition  is  but  seldom  found,  but 
as  it  gives  safe  values,  its  assumption  is  justified. 

When  a  bank  of  such  sand  has  an  unrestricted  surface  its  sides 
will  assume  a  natural  slope  of  about  11/2  feet  horizontal  to  i  foot 
vertical.  This  is  referred  to  as  the  "  Angle  of  Repose,"  or  "  Angle 
of  Friction." 

If  a  wall  is  placed  at  the  edge  of  a  bank  and  the  space  between 
the  back  of  the  wall  and  the  bank  filled  in,  this  earth  or  "back- 
ing "  will  tend  to  slide  along  the  line  of  repose,  and  thus  produce 
a  pressure  against  the  wall.  The  upper  half  of  this  prism  is  con- 
sidered as  producing  the  maximum  pressure  effect  on  the  wall  and 
its  weight  is  employed  in  computing  this  pressure. 

Effect  of  Earth  Pressure. — Mathematical  investigations  have 
determined : 

I.  That  the  entire  effect  of  this  pressure  may  be  considered  as 
concentrated  at  a  point  1/3  the  height  from  the  bottom. 

II.  That  this  pressure  will  tend   to   either  slide  or  push  the 
wall  bodily  out  of  place,  or  to  rotate  it  about  its  toe  and  overturn, 
or  both. 

III.  That  since  the  wall  is  rigidly  constructed  and  cannot  yield, 
the  effect  of  the  external  pressure  is  to  induce  strains  in  the  material 
of  the  wall. 

IV.  That  the  material  of  the  wall   can  resist   safely  certain 
specified  strains  per  unit  of  area  of  material  such  as  the  square  inch 
or  square  foot,  the  amount  of  such  safe  strains  varying  with  the  kind 
of  strain  and  the  material. 

V.  That  the  foundation  material  must  not  be  subjected  to  un- 
safe strains.    From  these  assumed  conditions  the  dimensions  of  the 
wall  are  fixed  so  that  the  strain  in  the  material  will  never  exceed  what 
it  can  safely  stand.     It  is  thus  seen  that  the  following  methods 
of  failure  are  possible. 

Methods  of  Failure. — A  retaining  wall  may  fail  in  one  or  more 
of  the  following  ways: 

i.  By  revolving  about  any  horizontal  line  in  the  face.  This  is  the 
most  frequent  mode  of  failure,  and  it  is  due  to  the  overturning 
moment,  due  to  the  earth  backing  being  greater  than  the  righting 
jnornent  of  the  wall  itself.  A  failure  of  this  type  indicates  too  light 


Concrete    Retaining    Walls 

a  wall  for  the  work  imposed  upon  it  or  too  heavy  a  load  on  the  soil 
at  the  base  of  the  wall. 

A  wall  which  shows  signs  of  failure  by  this  method  may  be 
strengthened  by  buttressing. 

2.  By   Sliding   on   any   Horizontal  Plane. — This   is   the   least 
frequent  method  of  failure,  and  in  a  monolithic  wall  free  from  all 
horizontal   joints   as   is  the   case  in  a  wall  of   concrete,  is   prac- 
tically impossible  except  by  the   sliding  of  the  entire  wall  on  its 
foundation  bed.      This  is  a  rare  occurrence,  and  when   it  occurs 
is  probably  the  result  of  the  wall  having  been  founded  on   an 

.  unstable  material,  perhaps  an  inclined  bed  of  moist  and  uncer- 
tain soil.  When  the  foundation  rests  upon  piles,  a  simple  expe- 
dient is  to  drive  piles  in  front  of  and  against  the  edge  of  the 
foundation.  When  the  foundation  rests  on  rock,  the  resistance 
to  sliding  may  be  increased  by  leaving  the  surface  of  the  bed 
rough,  or  in  case  the  rock  quarries  out  with  smooth  surfaces, 
the  bed  of  the  foundation  may  be  channelled  longitudinally,  and 
the  channels  afterward  filled  with  masonry.  In  case  of  the  wall 
resting  on  earth,  increasing  the  depth  of  the  foundation  below 
the  ground  level  at  the  face  of  the  wall,  thereby  increasing  the 
area  against  which  the  face  of  the  wall  abuts,  greatly  increases  its 
stability  against  sliding. 

3.  By  the  Bulging  of  the  Body  of  the  Masonry. — This  form  of 
failure  can  occur  only  in  walls  restrained  at  both  top  and  bottom, 
as  in  cellar  walls,  some  abutments,  walls  with  land  ties,  etc.      A 
failure  of  this  type  indicates  too  light  a  design. 

Some  of  the  causes  of  failure  of  retaining  walls  which  cannot 
readily  be  taken  care  of  in  computation  are :  settlement  of  founda- 
tion, bulging  due  to  poor  drainage,  formation  of  ice,  etc.  These 
must  be  looked  after  in  the  plans  and  construction  and  will  be 
referred  to  later. 

Types  of  Retaining  Walls. — Concrete  retaining  walls  are  con- 
structed in  three  general  types,  depending  upon  local  conditions 
and  often  upon  the  mood  of  the  designer.  These  are: 

I.  Gravity  walls,  with  or  without  reinforcement  which  depend 
for  their  stability  entirely  upon  the  weight  of  concrete. 

II.  Reinforced-concrete  cantilever  walls    of  uniform  thickness 
and  wide  reinforced  base  footing. 

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Handbook  for  Cement  and  Concrete  Users 

III.  Reinforced-concrete  walls  having  buttresses  at  regular 
intervals  on  the  rear  face  of  the  walls. 

Gravity  Retaining  Walls.— The  gravity  wall  is  adapted  for  low 
banks  or  fills  as  in  any  large  work  the  amount  of  concrete  necessary 
to  give  the  required  weight  makes  it  very  costly.  In  such  cases 
the  reinforced-concrete  wall  is  always  employed. 

In  the  gravity  wall  the  side  subjected  to  pressure  is  stepped,  and 
the  exposed  side  slopes  away  from  the  bank  to  give  increased  stability. 

It  is  an  important  principle  of  mechanics  that  the  resultant  of 
all  forces  acting  on  a  wall  should  never  pass  outside  of  the  middle 
third  of  the  cross-section,  and  it  is  in  order  to  follow  this  principle 
that  the  outside  of  the  wall  is  stepped  or  sloped.  By  following  this 
principle,  no  tensional  or  pulling  stresses  develop  in  the  plain  con- 
crete which,  by  assumption,  it  cannot  safely  carry. 

This  principle  holds  true  in  all  homogeneous  masonry  structures. 

Design  of  Gravity  Walls. — The  design  of  the  gravity  wall  is 
usually  a  rather  simple  matter,  as  it  is  only  necessary  to  assume  a 
width  of  base  of  about  .4  of  the  height.  Make  it  2  feet  or  up, 
wide  on  the  top,  according  to  practical  requirements,  and  then 
compute  its  weight  .and  the  pressure  due  to  the  earth  backing  (or 
water  in  case  of  a  dam),  and  compare  the  effect  of  this  pressure  to» 
produce  sliding  and  rotation,  with  the  power  of  resistance  as  deduced 
from  the  weight.  If  the  .latter  is  greater,  the  wall  is  theoretically 
safe. 

The  steps  followed  in  the  theoretical  design  of  a  gravity  retaining 
wall  are  well  outlined  in  Lewis  and  Kempners'  Manual  of  Examina- 
tions, as  follows: 

1.  The  height  of  the  wall  is  determined  by  local  conditions. 

2.  Assume  total  thickness  of  wall. 

1/5  the  height  at  top. 
2/5  the  height  at  bottom. 

3.  Plot  the  wall  to  scale. 

4.  Compute  the  weight  of  the  maximum  earth  prism.     Also 
compute  the  thrust  of  same,  which  equals'  about  .64  of  this  weight. 
(Earth  weighs  100  Ibs.  per  cu.  ft.) 

5.  Compute  weight  of  wall — concrete  weighing  about  140  Ibs. 
per  cu.  ft.     Also  compute  position  of  centre  of  gravity. 


Concrete    Retaining    Walls 

6.  Draw  to  scale,  the  line  of  thrust  making  an  angle  equal  to 
the  angle  of  friction   with  the  normal  to  the  back  of  the  wall  (see 
Fig.  77),  and  passing  through  the  centre  of    pressure,  which    is 
i/3  of  the  height  from  the  bottom. 

7.  To  same  scale  draw  line  representing  weight  of  wall  through 
its  centre  of  gravity. 

8.  Combine  these  as  shown.     The  resulting  pressure  line  should 
fall  within  the  middle  third  of  the  base  to  insure  absence  of  tension 
in  the  joints. 

9.  Compute    the    overturning    moment    due    to    thrust.     Also 
compute   resisting  moment   of  the   wall.     The   resisting  moment 
should  exceed  the  overturning  moment  by  a  safe  margin. 


FIG.  77. — Diagram  Showing  Forces  Acting  on  Gravity  Retaining  Wall. 

10.  Compute  the  horizontal  thrust,  also  frictional  resistance  to 
sliding  (weight  X  coefficient  friction).     The  latter  should  be  equal 
to  or  exceed  3  times  the  former. 

11.  Test  security  of  foundation  by  computing  unit  load  at  the 
toe  (total  load  per  running  foot  divided  by  1/2  width  of  base). 

All  conditions  of  stability  must  be  satisfied  and  all  unit  loads 
should  be  within  safe  limits;  if  not,  change  dimensions  and  recom- 
pute. 

REINFORCED-CONCRETE  WALLS 

Reinforced-concrete  walls  are  designed  along  different  lines. 
The  external  loading  is  the  same  as  in  the  gravity  wall,  but  the  wall 
itself  and  the  buttresses  are  considered  as  cantilever  slabs  or  beams 

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Handbook  for  Cement  and  Concrete  Users 


supported  at  the  bottom  only,  and  the  stresses  figured  somewhat 
in  the  same  way  as  in  the  beam  or  slab  computations.  The  footing 
is  also  considered  as  an  inverted  cantilever  beam  or  slab  with  the 
pressure  acting  upward  against  it,  tending  to  rupture  it  at  the 
junction,  and  the  proportions  of  steel  and  concrete  must  be  so 
arranged  as  to  prevent  unsafe  strains  from  being  developed. 

Reinforced-concrete  walls  do  not  depend  upon  the  weight  of  the 
masonry  alone  to  resist  overturning,  but  utilize  also  the  weight  of 
the  earth  backing  resting  on  the  base  of  the  wall. 

The  economy  of  a  reinforced-concrete   retaining  wall  is   due 


80 

FlG.  78. — Reinforced  Concrete  Retaining  Wall.  FIG.  79. — Reinforced  Concrete 
Retaining  Wall  with  Counterfort.  FIG.  80. — Reinforced  Concrete  Retaining  Wall 
with  Counterfort  and  Centre  Platform. 

chiefly  to  the  utilization  of  the  downward  pressure  of  the  backing 
in  resisting  overturning. 

In  reinforced-concrete  retaining  walls  as  in  masonry  ones,  pro- 
visions must  be  made  against  sliding,  and  the  wall  must  have  a 
suitable  foundation. 

Classes  of  Reinforced-Concrete  Walls. — Reinforced-concrete 
retaining  walls  may  be  divided  into  three  classes :  i.  Walls  without 
counterforts;  2.  Walls  with  counterforts;  3.  Walls  restrained  at 
top  and  bottom. 

Walls  without  Counterforts. — This  type  is  generally  economical 
for  walls  of  low  or  medium  height.  More  material  is  used  than  in 


Concrete    Retaining    Walls 

a  wall  with  counterforts,  but  the  decreased  cost  of  form  work  and  of 
placing  the  reinforcing  and  concrete  will,  in  a  wall  of  average  height, 
more  than  offset  the  cost  of  the  extra  material. 

These  walls  are  simple  in  form,  consisting  of  a  thin  reinforced 
vertical  wall  rigidly  attached  to  a  base  formed  by  a  reinforced- 
concrete  slab.  The  vertical  wall  acts  as  a  cantilever,  with  its 
maximum  bending  moment  at  the  upper  face  of  the  base.  This 
also  is  the  point  of  maximum  shear,  and  the  vertical  wall  should  be 
designed  accordingly.  As  the  bending  moment  and  shear  de- 
crease, as  the  top  of  the  wall  is  approached,  the  thickness  of  the 
wail  and  the  amount  of  reinforcing  may  also  be  decreased.  The 
base  at  the  heel  also  acts  as  a  cantilever,  and  must  resist  the  weight 
of  the  earth  resting  upon  it.  The  moment  and  shear  are  maximum 
at  the  rear  of  the  vertical  wall  and  the  base  should  be  designed 
accordingly.  The  toe  of  the  wall  also  acts  as  a  cantilever  resisting 
the  upward  thrust  of  the  earth  caused  by  the  tendency  of  the  wall 
to  overturn.  It  takes  its  maximum  moment  and  shear  at  the  face 
of  the  vertical  wall. 

Walls  with  Counterforts. — These  walls  consist  of  a  broad  base, 
a  thin,  vertical,  curtain  wall,  and  ribs  or  counterforts  spaced  3  to 
10  feet  on  centres,  connecting  the  base  with  the  vertical  wall. 

This  type  of  wall  is  very  economical  of  material,  and  this  economy 
increases  in  proportion  to  the  height.  The  cost  of  form  work, 
however,  is  great,  and  except  in  the  case  of  high  walls,  the  wall 
without  counterforts  is  generally  more  economical. 

In  this  type  of  wall  the  bending  moment  produced  by  the  earth 
pressure  is  resisted  entirely  by  the  counterforts.  The  vertical  wall 
acts  like  a  floor  slab  and  transmits  the  horizontal  earth  pressure  to 
the  counterforts.  The  base  at  the  back  of  the  wall  also  acts  as  a 
floor  slab,  carrying  the  weight  of  the  earth  above  it,  and  serving  as 
an  anchorage  to  the  counterforts.  That  portion  of  the  base  in  front 
of  the  vertical  wall  should  be  designed  as  a  cantilever,  fixed  into  the 
wall,  and  resisting  the  upward  pressure  of  the  earth,  caused  by 
the  tendency  of  the  wall  to  overturn. 

The  counterforts  should  be  designed  to  take  care  of  all  stresses 
due  to  overturning.  Sufficient  horizontal  and  vertical  reinforcing 
rods  should  be  placed  in  the  counterforts  to  properly  tie  them  to  the 
face  wall  and  base. 


Handbook  for  Cement  and  Concrete  Users 

In  the  foregoing  types  of  walls  the  walls  should  be  so  proportioned 
that  the  maximum  pressure  at  the  toe  does  not  exceed  the  safe  bear- 
ing value  of  the  soil. 

Walls  Restrained  at  Top  and  Bottom. — Cellar  walls  and  walls 
with  land  ties  are  of  this  type.  They  may  consist,  in  a  cellar  wall,  of 
a  slab  reinforced  vertically  to  withstand  the  pressure  of  the  earth 
backing,  and  supported  by  the  adjacent  floors,  or  the  slab  may  be 
reinforced  horizontally  carrying  the  load  to  vertical  beams  which  in 
turn  are  supported  by  the  adjacent  floors. 

A  wall  with  land  ties  is  similar  with  the  exception  that  a  horizontal 


8 1  82  83 

FIGS.  81,  82,  83. — Sections  of  Typical  Types  of  Concrete  Foundation  Walls. 

girder  extending  from  tie  to  tie  is  necessary  to  properly  deliver  the 
load  to  the  land  tie.  The  resistance  to  sliding  in  a  wall  of  this  type 
depends  on  frictional  resistance  and  the  abutting  power  of  the  earth 
in  front  of  the  face  at  its  toe. 

Details  of  Construction. — In  the  construction  of  retaining  walls, 
of  both  plain  and  reinforced  concrete,  the  same  general  rules  apply 
as  to  quality  of  material,  details  of  form  work,  placing,  and  in- 
spection, as  are  given  for  other  structures;  the  difference  between 
the  plain  and  reinforced  concrete  being  that  in  the  former  a  much 
larger  aggregate  can  be  used  both  for  the  purpose  of  adding  weight 
and  saving  cement,  and  it  is  excellent  practice  in  the  construction  of 
large  gravity  walls,  to  employ  a  rubble  concrete,  or  to  embed  in 
successive  layers  of  concrete  large  blocks  of  stone. 


Concrete    Retaining    Walls 

The  special  points  which  must  be  looked  for  in  the  construction 
of  retaining  walls  of  any  type  are : 

1.  The  preparation  of  a  secure  and  satisfactory  foundation  below 
the  frost  line  (2  to  4  feet,  depending  upon  the  climate). 

2.  The  drainage  of  the  foundation  and  removal  of  springs,  etc., 
under  same.     Removal  of  poor  material,  stepping  of  rock  surfaces, 
etc. 

3.  The  construction  of  a  drainage  system  behind  and  adjacent 
to  the  back  of  the  wall,  by  means  of  gravel,  channels,  or  other  means 
and  outlets,  as  weepers  or  pipes  through  the  wall  to  carry  off  the 
water. 

4.  The  compacting  of  the  material  or  backing  behind  the  wall 
(except  that  immediately  adjacent)  to  reduce  the  pressure  on  same 
as  much  as  possible. 

5.  The  construction  of  a  substantial  coping  along  the  top  of  the 
wall. 

6.  Expansion  joints   should   extend  through  the   walls   either 
directly  or  by  means  of  special  connections  to  prevent  temperature 
cracks.     These  may  be  20  to  30  feet  apart  in  plain  concrete  walls 
and  40  to  50  apart  in  reinforced  walls,  the  reinforcement  helping 
materially  to  avoid  such  cracks.    Five  per  cent  additional  reinforce- 
ment will  usually  be  sufficient  for  this  purpose. 

Foundations  for  Retaining  Walls. — The  management  of  the 
foundation  of  a  retaining  wall  is  an  important  matter,  and  it  is 
generally  admitted  that  a  large  majority  of  the  failures  of  retaining 
walls  are  due  to  defects  in  the  foundations.  The  nature  of  the  soil 
should  first  be  determined,  and  tests  made  to  ascertain  its  bearing 
capacity,  and  the  wall  then  so  proportioned  that  no  portion  of  the 
soil  shall  be  overloaded.  If  necessary,  the  bearing  capacity  of  the 
soil  may  be  increased  by:  i.  deeper  excavation;  2.  drainage;  3. 
consolidating  the  soil;  or,  4.  by  means  of  sand  piles.  If  none  of 
the  above  methods  give  satisfactory  results,  piles  of  either  timber 
or  reinforced  concrete  must  be  used.  If  the  foundation  is  on  rock 
it  is  only  necessary  to  cut  away  the  loose  and  decayed  portion  of  the 
rock  and  to  dress  it  to  a  plane  as  nearly  perpendicular  to  the  direction 
of  the  pressure  as  possible,  any  fissures  being  filled  with  concrete. 
Other  methods  of  providing  adequate  foundations  are  described  in 
Chapter  XXI. 

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Drainage. — Next  to  faulty  foundations,  water  behind  the  wall 
is  the  most  frequent  source  of  failure  of  retaining  walls.  The  water 
not  only  adds  to  the  weight  of  the  backing  material,  but  also  softens 
the  material  and  causes  it  to  flow  more  readily,  thus  greatly  increasing 
its  lateral  thrust.  To  guard  against  the  possibility  of  the  backing 
becoming  saturated  with  water,  holes,  called  weep  holes,  are  left 
through  the  wall.  The  holes  should  be  spaced  generally  from  i 
to  3  sq.  yds.  of  face  of  wall.  When  the  backing  is  clean  sand  the 
weep  holes  will  allow  the  water  to  escape;  but  if  the  backing  is 
retentive  of  water,  blind  drains  should  be  placed  in  back  of  the  wall 
and  lead  the  water  to  the  weep  holes. 

Land  Ties. — Retaining  walls  may  have  their  stability  increased  by 
being  anchored  to  a  suitable  anchorage  embedded  in  a  firm  strata  of 
earth  a  distance  behind  the  wall.  The  amount  of  load  taken  by 
these  rods  will  depend  on  their  position  in  the  face  of  the  wall.  If 
they  are  fastened  to  the  wall  at  the  top,  they  will  take  one-third  of  the 
total  earth  pressure.  If  they  are  fastened  in  the  wall  at  one-third 
the  height  from  the  top,  they  will  take  one-half  the  total  pressure. 

Relieving  Arches. — In  extreme  cases  the  pressure  of  the  earth 
may  be  sustained  by  relieving  arches.  These  consist  of  one  or 
more  rows  of  arches  having  their  axes  at  right  angles  to  the  face  of 
the  bank  of  earth.  Their  front  ends  may  not  be  closed,  which  then 
prevents  the  appearance  of  a  retaining  wall,  although  the  length  of 
the  archway  is  such  as  to  prevent  the  earth  from  abutting  against 
the  wall. 

Concrete  Abutments. — An  abutment  has  two  offices  to  perform: 
i.  to  support  one  end  of  a  bridge;  2.  to  act  as  a  retaining  wall. 

There  are  four  forms  of  abutments  in  more  or  less  general  use : 

1.  A  straight  abutment — a  plain  wall  with  or  without  wings. 

2.  Wing  abutment — wing  walls  make  an  angle  with  the  face  of 
the  abutment  (usually  about  30  degrees). 

3.  U-abutment — when  the  ring  makes   an^  angle  of  90  degrees 
with  the  face  of  the  abutment. 

4.  T-abutment — when  the  wings  are  moved  to  the  centre  of  the 
abutment  and  merged  into  one  stem. 

The  dimensions  of  an  abutment  are  to  be  determined  as  for  a 
retaining  wall.  These  dimensions  must  be  such  that  the  abutment 
can  safely  carry  the  superimposed  load. 

[254] 


Concrete    Retaining    Walls 


The  form  of  abutment  adopted  in  any  case  will  depend  on  the 
locality.  If  the  shore  is  flat,  and  not  liable  to  be  cut  away  by  the 
current,  a  straight  abutment  will  be  sufficient  and  most  economical. 
However,  this  form  is  seldom  used  owing  to  the  danger  of  the  water 
flowing  along  immediately  behind  the  wall. 

When  there  is  a  contraction  of  the  waterway  at  the  bridge  site, 
a  wing  abutment  may  be  adopted,  since  the  deflecting  wing  walls, 
above   and    below,   slightly    in- 
crease   the    amount    of    water 
that  can  pass. 

The  use  of  U-  and  T-abut- 
ments    seems   to   be   mainly   a 
matter   of    choice.      To    equal 
amounts  of  masonry  wing  abut- 
ments give  better  protection 
to    the    embankment    than 
either    U-  or  T-abutments. 
The  latter  are  more  stable, 
as  the  centre   of   gravity   of 
the  masonry  is  farther  back  from 
the  line  of   the  face  of   the  abut- 
ment,    about     which      line     the 
abutment     will      turn     or    along 
which  it  will  crash. 

Reinforced  -  Concrete  Abut- 
ments. —  When  reinforced  con- 
crete is  used  to  replace  masonry 

in  abutments  a  considerable  reduction  in  cost  will  result.  The 
construction  usually  consists  of  a  rectangular  slab  for  a  base, 
whose  width  will  depend  on  the  load  to  be  distributed.  Counter- 
forts transmit  the  load  from  the  bridge  seat  to  the  base.  A  face 
wall  heavy  enough  to  resist  the  earth  pressure  is  firmly  anchored 
to  the  counterforts.  The  face  wall  may  continue  beyond  the  bridge 
seat  so  as  to  form  wing  walls,  which  in  reality  are  nothing  more  or 
less  than  retaining  walls.  The  bridge  seat  consists  of  a  heavy 
reinforced-concrete  slab  supported  by  the  counterforts.  A  parapet 
wall  at  the  back  and  ends  of  the  bridge  seat  forms  the  mud  wall. 
The  construction  and  design  of  the  reinforced-concrete  abutments 

[255] 


FIG.  84. — Forms  of  Concrete 
Abutments. 


Handbook  for  Cement  and  Concrete  Users 

closely  resemble  the  construction  and  design  of  a  reinf orced-concrete 
retaining  wall,  with  the  exception  of  the  bridge  seat  and  supporting 
counterforts.  It  is  desirable,  if  possible,  to  place  the  main  but- 
tresses directly  under  the  girders  or  trusses,  thereby  eliminating 
bending  in  the  slab  forming  the  bridge  seat. 

Bulkheads. — Bulkhead  walls  are  essentially  retaining  walls 
having  a  large  portion  of  their  depth  under  water.  This  makes  the 
calculation  of  their  dimensions  much  more  complicated  than  the 
ordinary  wall,  and  the  computations  are  still  further  complicated 
by  the  varying  densities  of  the  materials  adjacent  to  the  wall. 


FIG.  85. — Reinforced  Concrete  Abutment. 

In  Fig.  86    is   shown  a  typical  section  of  a  bulkhead  wall  ex- 
tensively employed  in  New  York  City. 
The  forces  acting  for  stability  are : 

1.  The  weight  of  the  submerged  portion  of  the  wall. 

2.  The  weight  of  the  exposed  portion  of  the  wall. 

3.  The  vertical  pressure  of  the  water. 
The  forces  acting  against  stability  are: 

1.  The  horizontal  pressure  of  the  water. 

2.  The  pressure  of  the  earth  filling. 

3.  The  live  load  on  the  wall. 

The  amount  and  position  of  the  resultant  pressure  of  all  these  op- 
posing forces  must  be  found  in  order  to  properly  proportion  the  wall. 

The  type  of  bulkhead  wall  depends  upon  the  character  of  the 
foundation. 

On  rock  foundations  the  area  is  dredged  and  the  rock  cleaned 
and  stepped  off  when  too  smooth.  Concrete  is  deposited  in  accord- 
ance with  methods  outlined  in  Chapter  VII.  Divers  then  smooth 
off  the  surface  with  mortar  to  receive  the  concrete  blocks.  These 
blocks  weight  about  70  tons,  being  17X6X12  feet. 

Upon  these  heavy  foundation  blocks,  granite  with  concrete 
backing  is  laid,  and  the  riprap  deposited  as  filling. 

[256] 


Concrete    Retaining    Walls 


The  Hennebique  Construction  Company  and  several  others 
have  patented  methods  of  building  bulkhead  walls  of  reinforced 
concrete  by  constructing  portions  on  shore,  floating  them  to  place 
and  sinking  by  depositing  concrete  in  prepared  chambers.  While 
the  method  has  been  employed  in  Europe,  it  has  as  yet  been  little 
tried  in  this  country: 

Appearance  of  Retaining  Walls. — While  the  object  of  the  retain- 
ing walls  mainly  is  utility,  pleasing  and  aesthetic  appearance  may 


FIG.  86.— Concrete  Blocks  in  New  York  City  Bulkheads. 

be  obtained  at  but  slight  additional  cost,  and  often  at  no  additional 
cost  whatever.  The  maintenance  of  a  pleasing  surface  once 
obtained  depends  upon  the  construction  and  materials  in  and  about 
the  walls.  We  frequently  see  long  stretches  of  carefully  shaped 
and  built  walls  disfigured  by  rust  and  smoke  stains,  efflorescence, 
checks,  and  cracks,  and  other  disagreeable  causes.  In  most  cases 
these  may  be  avoided  by  the  use  of  a  rough  instead  of  smooth 
surface  finish,  and  the  avoidance  of  ironwork  above  the  wall,  the 
rust  from  which,  carried  down  by  water,  is  the  cause  of  the  rust 
stains.  Efflorescence  may  largely  be  avoided  by  adding  a  small 

i?  [257] 


Handbook  for  Cement  and  Concrete  Users 

percentage  of  water-repellant  compound  to  the  cement  in  the 
concrete  placed  against  the  exposed  surface  forms.  This  will 
render  the  surface  water-repellant  and  prevent  absorption  during 
rainstorms,  which  bring  out  the  stain.  t 

The  prevention  of  percolation  of  water  through  walls  and 
arches  is  frequently  desirable  and  is  readily  effected  by  enveloping 
the  structure  in  a  2  or  more  ply  bituminous  shield,  using  the  mem- 
brane method  as  described  in  the  chapter  on  waterproofing. 

With  this  on  the  earth  side,  and  the  surface,  water-repellant, 
the  wall  will  maintain  its  fresh  appearance  if  iron  work  above  it  is 
avoided,  or  proper  drainage  from  same  provided,  and  if  a  crack- 
free  surface  has  been  obtained. 

The  disfigurement  by  smoke  and  locomotive  gases  can  be  avoided 
only  in  one  way:  by  giving  the  face  of  the  wall  a  dark  color 
during  construction  so  that  such  staining  will  not  be  noticeable. 
Considering  the  large  amount  of  money  spent  by  the  railroads  to 
obtain  pleasing  effects  in  concrete  work,  it  seems  wrong  to  construct 
surfaces  which  particularly  invite  such  disfigurement  from  the  very 
start. 


[258] 


Concrete    Retaining    Walls 


TABLE  XXII.— EARTH  PRESSURES.* 

Angle  of  Repose  =  0  =  33  Degrees. 


Depth, 
in  ft. 

'  Total 
Inclined 
Press. 

Total 
Hor.  Press, 
per  lin.  ft. 

Hor.  Press, 
per  Square 
Foot. 

Depth, 
in  ft. 

Total 
Inclined 
Press. 

Total 
Hor.  Press, 
per  lin.  ft. 

Hor.  Press, 
per  Square 
Foot. 

5 

335 

280 

112 

23 

7080 

5935 

5i6 

6 

480 

405 

135 

24 

7710 

6460 

538 

7 

655 

55° 

157 

25 

8365 

7OI5 

56i 

8 

855 

720 

1  80 

26 

9°45 

7585  ' 

583 

9 

1085 

910 

202 

27 

9755 

8180 

606 

10 

1340 

II2O 

224 

28 

10490 

8800 

628 

n 

1620 

1355 

246 

29 

11255 

9435 

650 

12 

1930 

1615 

269 

3° 

12040 

IOIOO 

673 

r3 

2260 

1895 

291 

31 

12860 

10780 

696 

14 

2625 

22OO 

3*4 

32 

13700 

11490 

718 

15 

3010 

2525 

337 

33 

1457° 

I222O 

741 

16 

3425 

2870 

359 

34 

15455 

12960 

763 

J7 

3865 

3245 

38i 

35 

16390 

!3745 

785 

18 

4335 

3635 

404 

36 

17340 

14540 

808 

*9 

4830 

4050 

426 

37 

18315 

i536o 

830 

20 

5350 

449° 

449 

38 

19320 

16200 

853 

21 

5900 

495° 

471 

39 

20350 

17065 

875 

22 

6475 

543° 

493 

40 

21410 

17950 

896 

cos  0  eh2 


=  .  i33Seh?  for  0=33° 


Earth  Level. 

Total  Inclined  Pressure  = 

2(1  +  sin  0  \/2) 

Total  Hor.   Pressure  =  11.22  h2  acting  at  depth  =  2/3  h. 
Note. — e  =  100  Ibs.  per  cu.  ft.;  h  =  depth  in  feet. 

TABLE  XXIII. 

THICKNESSES  or  WALLS  AND  QUANTITIES  or  MATERIALS  FOR  DIFFERENT 
HEIGHTS  OF  BASEMENTS. 


Proportions: 


i  Part  Portland  Cement  to  2^  Parts  of  Sand  to  5  Parts  of  Gravel 
or  Stone. 


Height 
of 
Basement. 

Depth  of 
Foundation 
Below 
Ground 
Level. 

Thickness 
of  Wall 
at  Bottom. 

Thickness 
of  Wall 
at  Top. 

Cement  per 
10  Feet  of 
Length  of 
Wall. 

Sand  per 
10  Feet  of 
Length  of 
Wall. 

Gravel  or 
Stone  per 
10  Feet  of 
Length  of 
Wall. 

Feet. 

Feet. 

Inches. 

Inches. 

Bags. 

Cubic  Feet. 

Cubic  Feet. 

6 

4 

6 

6 

6 

14  l/a 

29 

8 

6 

10 

8 

12 

29 

58 

10 

8 

15 

10 

24 

57 

114 

*  Trussed  Steel  Concrete  Co. 

[259] 


Handbook  for  Cement  and  Concrete  Users 


TABLE  XXIV. — DIMENSIONS  OF  GRAVITY  RETAINING  WALLS 
AND  QUANTITY  OF  MATERIALS  FOR  DIFFERENT  HEIGHTS  OF 
WALLS.* 

Proportions:     i  Part  Portland  Cement  to  2^  Parts  Sand  to  5  Parts  Gravel  or  Stone. 


Qi 

Is 

*o 

^-J 

| 

AMOUNT  OP  MATERIALS  PER  ONE 

>  § 

j3 

ct 

Oj    > 

r^ 

FOOT  LENGTH  OF  WALL. 

«-.  S 

•5?=: 

i  a? 

Mh-5 

"rt 

"GO 

^  oj 

C-  M 

C  Tl 

t/5 

-u  " 

Ew  ^ 

rX  £Q 

^c 

0) 

11 

1 

g 

.a  s 

9 

H 

Cement. 

Sand. 

Gravel 
or 
Stone. 

Feet. 

Feet. 

Ft.     In. 

Ft.      In. 

Inches. 

Bags. 

Cu.  Ft. 

Cu.  Ft. 

2 

6 

2         2 

i       6 

10 

if 

4K 

9 

3 

7 

2      5 

i       7K 

IO 

2K 

5^ 

ii 

4 

8 

2       9 

i     ii 

12 

3 

7 

14 

5 

9 

3       2 

2           I 

12 

3K 

9 

18 

6 

10 

3       6 

2          4M 

15 

4f 

ii  K 

23 

7 

ii 

3     1° 

2          8 

18 

6 

14 

28 

8 

12 

4       2 

2        10 

18 

7 

16* 

33 

FIG.  87. — Section  of  Gravity  Retaining  Wall 


Note. — A  large  single  load  of  sand  or  gravel  is  about  20  cu.  ft. 

A  large  double  load  of  sand  or  gravel  is  about  40  cu.  ft. 

*  From  "  Concrete  Construction  about  the  Home  and    on  the  Farm,"  published 
by  the  Atlas  Portland  Cement  Co, 

[260] 


CHAPTER  XXIII 

CONCRETE    ARCHES    AND    ARCHED    BRIDGES 

Definitions. — Parts  of  an  Arch. — Methods  of  Failure. — Design  of  an  Arch. — Abut- 
ments and  Piers. — Reinforced-Concrete  Arches. — Arch  Bridges. — Arch  Centres. 
— Concreting  the  Arch. 

THE  value  of  the  arch  as  a  structure  of  great  beauty  and  economy 
has  been  known  for  many  thousands  of  years,  and  while  many  elabo- 
rate arches  have  been  constructed  of  the  finest  stones,  it  has  remained 
for  the  present  generation  to  see  arches  of  masonry  of  such  light 
sections  and  such  beautiful  lines  as  to  challenge  the  admiration  of 
observers.  This  combination  of  beauty,  lightness,  and  consequent 
economy  has  been  rendered  possible  only  by  combining  in  the  arch 
the  resisting  power  of  steel  in  tension  and  of  concrete  in  compression, 
as  described  in  this  chapter. 

DEFINITIONS— PARTS  OF  AN  ARCH 

Soffit. — The  inner  or  concave  surface  of  the  arch. 

Intrados. — The  line  of  intersection  between  the  soffit  and  a 
vertical  plane  normal  to  the  axis  of  the  arch. 

Extrados. — The  line  of  intersection  between  the  outer  surface 
of  the  arch  and  a  vertical  plane  normal  to  the  axis  of  the  arch. 

Crown. — The  highest  point  of  the  arch. 

Skewback. — The  inclined  surface  on  which  the  end  of  the  arck 
rests. 

Abutment. — A  skewback  and  the  masonry  which  supports  it. 

Springing  Line. — The  inner  edge  of  the  skewback. 

Haunch. — That  part  of  the  arch  between  the  crown  and  the 
skewback. 

Spandrel. — The  space  between  the  extrados  and  the  roadway. 

Spandrel  Filling. — Material  placed  on  top  of  arch  between 
spandrel  walls.  It  may  be  either  earth  or  masonry,  or  a  combina- 
tion of  both,  or  a  system  of  relieving  arches  which  carry  the  roadway. 


Handbook  for  Cement  and  Concrete  Users 

Span. — The  perpendicular  distance  between  springing  lines. 

Rise. — The  vertical  distance  between  the  highest  of  the  intrados 
and  the  plane  of  the  springing  line. 

Voussoirs. — The  wedge-shaped  stones  of  which  the  arch  is 
composed — also  called  arch  stones. 

Keystone.  — The  centre  or  highest  voussoir  or  arch  stone. 

Springer. — The  lowest  voussoir  or  arch  stone. 

Kind  of  Arches. — Circular  Arch. — One  in  which  the  intrados  is 
an  arc  of  a  circle. 

Semi-circular  or  Full-centred  Arch. — One  whose  intrados  is  a 
semi-circle. 

Segmental  Arch. — One  whose  intrados  is  an  arc  of  a  circle  but 
less  than  a  semi-circle. 

Elliptical  Arch. — One  whose  intrados  is  part  of  an  ellipse. 

Basket  Handle  Arch. — One  whose  intrados  resembles  a  semi- 
ellipse,  but  which  is  composed  of  arcs  of  circles  tangent  to  each 
other. 

Pointed  Arch. — One  in  which  the  intrados  consists  of  two  arcs 
of  equal  circles  intersecting  over  the  middle  of  the  span. 

Catenarian  Arch. — One  whose  intrados  is  a  catenary. 

Right  Arch.^Any  arch  terminated  by  two  planes  normal  to  the 
axis  of  the  arch. 

Skew  Arch. — Any  arch  terminated  by  two  planes  that  are  not 
normal  to  the  axis  of  the  arch. 

Groined  and  Cloistered  Arches. — Those  formed  by  the  inter- 
section of  two  or  more  arches,  each  having  the  same  rise,  and  with 
axes  in  the  same  planes. 

In  concrete,  only  right  arches  need  be  considered,  as  any  skew 
arch  may  be  regarded  as  composed  of  a  number  of  infinitely  short 
right  arches.  This  treatment  for  masonry  skew  arches  is  also  quite 
common  in  this  country,  the  arch  being  made  of  a  number  of  short 
right  arches  or  ribs,  in  contact  with  each  other,  but  with  each 
successive  rib  off  centre  slightly  from  the  preceding  one. 

Line  of  Resistance. — At  any  joint  in  an  arch  the  forces  acting 
may  be  replaced  by  a  single  force,  so  situated  as  to  be  in  every  way 
the  equivalent  of  the  distributed  forces  it  replaces.  The  line  con- 
necting the  points  of  application  of  these  forces  is  the  line  of  resist- 
ance of  the  arch. 

[262] 


Concrete  Arches  and  Arched  Bridges 

Methods    of    Failure. — An    archway    may    fail    in  any  of  the 
four  following  ways: 

1.  By  Crushing. — An  arch  will  fail  by  crushing  if  the  pressure 
on  any  part  is  greater  than  the  crushing  strength  of  the  material 
used.     This  may  be  caused  by  too  light    an   arch  being  designed 
or  by  the  line  of  resistance  passing  too  far  from  the  centre  line  of 
the  archway. 

2.  By  Sliding  of  One  Voussoir  on  Another. — An  arch  will  fail 
by  this  method  when  the  line  of  resistance  makes,  with  the  normal 
at  any  joint,  an  angle  greater  than  the  angle  of  friction  for  the  joint. 
This  type  of  failure  is  unlikely  in  a  concrete  arch,  as,  owing  to  its 
homogeneous  construction,  the  angle  of  friction  is  very  large. 


Tens/on 


FIG.  88.— Failure  of  Arch  by  Flattening  FIG.  89.— Failure  of  Arch  by  Flat- 

of  the  Crown.  tening  of  the  Haunches. 

3.  By  Rotation  About  the  Edge  of  Some  Joint. — If  the  arch  were 
incompressible,  failure  of  this  type  could  occur  only  when  the  line 
of  resistance  touched  the  intrados  at  two  points  and  the  extrados 
at  one  higher  intermediate  point,  or  vice  versa.     In  a  compressible 
arch,  and  all  masonry  arches  are  compressible,  failure  by  crushing 
would  probably  occur  before  the  conditions  necessary  for  failure 
by  rotation  could  be  realized. 

4.  Because   of  Unsatisfactory  Foundations. — More   arches   fail 
because  of  unsatisfactory  foundations  than  for  any  other  reason. 
Failure  of  this  type  is  due  either  to  unequal  settlement,  rotation,  or 
sliding  of  the  abutments. 

Design  of  an  Arch. — There  are  several  theories  for  the  design 
of  an  arch,  each  of  which  is  complex  and  at  best  only  an  approxima- 
tion. In  practically  all  theories  the  stability  of  the  arch  depends 
on  the  position  of  the  line  of  resistance.  The  position  of  the  line  of 
resistance  is  influenced  greatly  by  the  external  forces  acting  on  the 

[263] 


Handbook  for  Cement  and  Concrete  Users 

arch.  These  external  forces  may  be  divided  into  three  parts: 
i.  The  moving  or  live  load;  2.  The  permanent  or  dead  load,  which 
includes  the  weight  of  the  spandrel  filling  and  the  weight  of  the  arch 
itself;  3.  The  pressure  or  thrust  of  the  spandrel  filling.  This 
pressure  is  more  or  less  indeterminate.  In  the  case  of  the  spandrel 
filling  being  earth,  it  may  take  any  value  between  the  pressure  of 
earth  due  to  its  own  weight  only,  and  the  abutting  power  of  the 
earth. 

In  the  case  of  the  spandrel  filling  being  masonry,  the  value  of 
the  pressure  may  vary  between  the  limits  of  zero  and  the  working 
resistance  to  compression  of  either  the  backing  or  ring  stones. 

In  the  design  of  an  arch,  it  is  customary  to  limit  the  position  of 
the  line  of  resistance  to  the  middle  third  of  the  arch  ring,  in  which 
case  there  could  be  no  tension  in  the  ring,  and  therefore  no  tendency 
for  the  joint  to  open. 

It  does  not  follow,  however,  that  the  joint  will  necessarily  begin 
to  open  if  the  line  of  resistance  fall  outside  the  middle  third  of  the 
arch  ring,  or  that  the  stability  of  the  arch  is  necessarily  endangered. 
If  the  greatest  intensity  of  stress  does  not  exceed  the  ultimate  resist- 
ance to  compression  of  the  material,  there  can  be  no  opening,  except 
that  due  to  the  elasticity  of  the  material,  which  is  not  considered. 

Abutments  and  Piers. — As  before  stated,  most  arch  failures  are 
caused  by  the  failure  of  the  abutment  due  to  unsatisfactory  founda- 
tions. Such  failure  may  occur  in  either  of  three  ways:  i.  By 
overturning  of  the  abutment;  2.  By  sliding  of  the  abutment;  3. 
By  settling  of  the  abutment. 

1.  Failure  by  overturning  is  usually  caused  by  the  pressure  at 
the  base  of  the  abutment  exceeding  the  bearing  capacity  of   the 
soil.     A  failure  of  this  type  cannot  occur  when  the  line  of  resistance 
falls  at  the  centre  of  the  base,  as,  in  order  that  rotation  shall  take 
place,  the  pressure  on  the  soil  at  one  side  of  the  abutment  must  be 
larger  than  at  the  other. 

2.  Failure  by  sliding  of  the  abutment  is  caused  by  the  thrust  of 
the  arch  being  greater  than  the  sum  of  the  friction  between  the 
abutment  and  the  soil  on  which  it  rests,  and  the  pressure  of  the 
earth  behind  the  abutment.     In  an  extreme  case  where  the  abut- 
ment is  very  high,  the  pressure  of  the  earth  behind  the  abutment 
may  be  greater  than  the  thrust  of  the  arch  plus  friction  at  the  base 

[264] 


Concrete  Arches  and  Arched  Bridges 

of  the  abutment,  in  which  case  the  abutment  would  fail  by  sliding 
forward.  Hence,  for  a  large  arch  under  a  light  surcharge,  the 
abutment  should  be  proportioned  to  resist  the  thrust  of  the  arch; 
but  for  small  arches  with  a  heavy  surcharge,  the  abutment  should  be 
proportioned  as  a  retaining  wall. 

3.  Failure  by  settlement  of  the  abutment  implies  a  load  on  the 
foundation  greater  than  its  bearing  capacity.  This  load  on  the 
foundation  will  be  practically  uniform  as  otherwise  failure  would 
occur  by  the  overturning  of  the  abutment. 

As  a  safeguard  against  failure  in  a  masonry  arch,  it  is  necessary 
(i)  to  limit  the  position  of  the  line  of  resistance  to  the  middle  third 
of  the  arch  ring,  (2)  not  to  permit  the  unit  stress  to  exceed  in  inten- 
sity the  safe  crushing  strength  of  the  material  employed;  and  (3) 
not  to  allow  the  pressure  on  the  soil  to  exceed  its  safe  bearing  value. 

REINFORCED-CONCRETE  ARCHES 

While  concrete  is  a  more  economical  material  for  arches  than 
cut  stone  and  is  now  replacing  masonry  to  a  great  extent,  a  still 
greater  economy  may  be  realized  by  the  use  of  reinforcement. 

Design. — The  method  of  designing  an  arch  of  reinforced  concrete 
is  practically  the  same  as  that  employed  in  the  design  of  a  plain 
structure.  The  position  of  the  line  of  resistance  need  not,  however, 
be  so  rigidly  fixed  as  in  the  plain  arch ;  also  the  intensity  of  stress 
may  exceed  the  crushing  strength  of  the  concrete,  as  by  introducing 
sufficient  steel,  a  resistance  to  crushing  equal  to  this  higher  intensity 
may  be  easily  obtained. 

In  any  arch,  should  the  line  of  resistance  fall  outside  the  middle 
third  of  the  arch  ring,  tension  is  developed  at  one  end  of  the  joint 
and  an  increased  compression  at  the  other  end.  In  a  plain  concrete 
arch  the  tension  would  tend  to  open  cracks  in  the  arch,  as  previously 
described.  In  a  reinforced  arch,  this  tension  would  be  taken  by 
the  reinforcement  placed  there  for  that  purpose,  so  that  the  opening 
of  cracks  would  be  impossible. 

General  Types  of  Reinforced-Concrete  Arch  Bridges. — There 
are  two  types  of  reinforced-concrete  arch  bridges.  The  first  type, 
and  the  one  most  generally  used  in  this  country,  consists  of  an 
arched  slab,  the  full  width  of  the  bridge,  extending  from  abutment 

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Handbook  for  Cement  and  Concrete  Users 

to  abutment.  This  arched  slab  supports  the  spandrel  filling,  or 
the  system  of  relieving  arches,  which  in  turn  carries  the  roadway. 
This  type  of  arch  is  similar  in  all  respects  to  the  masonry  arch, 
except  that  owing  to  the  introduction  of  the  steel  reinforcement, 
higher  unit  stresses  may  be  permitted,  thus  making  a  longer  span 
possible. 

The  second  type  might  well  be  called  an  arched-rib  bridge. 
This  type  has  been  but  little  used  in  this  country,  but  has  been  ex- 
tensively employed  abroad,  particularly  in  France.  A  bridge  -of 
this  type  consists  of  a  series  of  heavily  reinforced  arched  ribs.  The 
ribs  support  a  series  of  columns,  which  in  turn  support  the  beams 
and  slabs  that  go  to  form  the  roadway.  This  type  of  bridge  is 
considerably  lighter  than  the  arched-slab  type  and  is  therefore 
more  economical  of  material.  The  cost  of  form  work,  however, 
is  higher. 

A  modification  of  the  arched-slab  type  of  bridge  is  the  Suten 
Arch.  The  difference  lies  in  the  horizontal  thrust  being  taken  up 
by  ties  between  the  abutments,  underneath  the  bed  of  the  stream 
which  are  embedded  in  concrete.  The  usual  heavy  abutments, 
where  the  foundation  is  not  of  rock,  are  thus  dispensed  with.  This 
system  of  tying  the  abutments  may  also  be  used  in  the  arched-rib 
type  of  bridge. 

Arches  of  the  above  types  may  be  built  either  as  continuous 
from  abutment  to  abutment,  or  as  two  or  three  hinged  arches. 
Either  style  of  construction,  if  properly  constructed,  will  give  entire 
satisfaction. 

The  advantages  of  a  reinforced-concrete  arch  may  be  sum- 
marized as  follows: 

(i)  Such  a  structure  is  more  economical  than  a  masonry  arch; 
(2)  the  cost  of  maintenance  is  less  than  that  required  for  a  steel 
bridge,  and  (3)  Its  life  is  longer  than  that  of  a  metal  structure. 
(4)  Its  light  weight  sometimes  makes  it  possible  to  construct  a 
reinforced-concrete  arch  where  a  masonry  arch  would  be  practically 
impossible.  (5)  The  materials  necessary  are  always  easily  obtain- 
able, and  usually  in  the  vicinity  of  the  work. 

Another  advantage  of  reinforced-concrete  arches  is  their  stiffness 
under  shocks,  and  the  small  deflection  under  heavy  loads.  This 
has  been  shown  repeatedly  in  actual  practice  and  in  special  tests. 

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[267] 


Handbook  for  Cement  and  Concrete  Users 

Perhaps  the  most  thorough  tests  in  this  line  were  those  carried  on 
at  the  bridge  at  Chatellnault,  Vienne,  France.  This  bridge  is  443 
ft.  long  and  composed  of  three  arches  whose  spans  are  135,  164,  and 
135  ft.,  respectively.  On  the  removal  of  the  forms  this  bridge  was 
subjected  to  the  following  test. 

1.  Each  day  the  spans  were  loaded,  first  over  their  total  length, 
then  on  each  half,  then  in  the  middle,  with  sand  at  the  rate  of  165 
Ibs.  per  sq.  ft.,  on  the.  roadway  and  123  Ibs.  per  sq.  ft.  on  the  side- 
walk.    The   maximum   deflections   under   these   loads   were,   end 
spans  1/4  inch  or  1/7300  of  the  span,  centre  arch  13/32  inch  or 
i  /  5000  of  the  span. 

2.  One  1 6-ton  steam  roller,  two  1 6-ton  two-axled  carts,  six  8-ton 
one-axled  carts,  total  weight,  including  horses,  100  tons,  passed  at 
once  over  the  bridge,  the  sidewalk  at  the  same  time  carrying  a  load 
of  80  Ibs.  per  sq.  ft. 

3.  250  soldiers  (infantry)   crossed    the  bridge,  first  in  regular 
marching  step,  second  in  double  time. 

The  maximum  deflection  under  these  tests  did  not  exceed 
1/9000  of  the  span,  and  all  vibration  ceased  almost  immediately  on 
the  removal  of  the  load. 

Arch  Centres. — A  centre  is  a  temporary  structure  for  supporting 
an  arch  while  in  process  of  construction.  It  is  usually  made  of  a 
number  of  circular  ribs  spaced  a  few  feet  apart,  and  lying  in  a  plane 
perpendicular  to  the  axis  of  the  arch.  These  ribs  are  covered  with 
narrow  planks  (lagging),  running  parallel  to  the  axis  of  the  arch, 
upon  which  the  arch  rests  while  in  course  of  construction.  In 
concrete  arches,  except  in  those  that  are  very  flat,  provision  for 
maintaining  the  extradosal  line  of  the  arch  must  also  be  made. 

All  centres  should  be  made  as  strong  and  as  rigid  as  possible, 
as  any  deformation  of  the  centre  due  to  insufficient  strength  or 
improper  bracing  will  cause  a  corresponding  change  in  the  intrados 
of  the  arch,  and  consequently  in  the  line  of  resistance,  and  may 
endanger  the  whole  structure. 

Arch  centring  in  general  may  be  divided  into  two  classes.  '  In 
the  first  class  the  ribs  are  supported  by  struts  braced  together  so  as 
to  form  transverse  bents.  These  bents  are  spaced  at  convenient 
distances  along  the  axis  of  the  arch  and  braced  longitudinally. 
Where  the  subsoil  is  sufficiently  firm,  the  struts  may  rest  on  mud 

[268] 


Concrete  Arches  and  Arched  Bridges 

sills,  but  in  poorer  soil  temporary  masonry  or  pile  foundations  are 
frequently  used. 

In  the  second  form  trusses  are  employed.  These  trusses  may 
carry  the  lagging  directly,  in  which  case  they  must  conform  to  the 
curve  of  the  intrados  of  the  arch,  or  they  may  support  short  braces 
which  in  turn  support  the  ribs.  Where  trusses  are  used  they  should 
be  cambered  slightly  so  that  after  deflection  the  arch  may  be  of  the 
desired  curvature. 

The  ribs  are  usually  made  of  planks  spiked  together  so  as  to 
break  joints,  and  cut  to  a  curve  parallel  to  the  intrados  of  the  arch, 
but  a  sufficient  distance  below  it  so  that  the  lagging,  when  applied, 


FIG.  91. — Centre  for  50  ft.  Arch  Span  (supported). 

shall  coincide  with  the  intrados  of  the  arch.     Sometimes  the  ribs 
are  steel  shapes  bent  to  the  desired  curvature. 

In  order  that  the  centres  may  be  struck,  or  lowered,  uniformly 
and  without  shock,  either  sand  boxes  or  wedges  are  used  under  all 
of  the  supports. 

The  wedges  usually  consist  of  a  pair  of  folding  wedges,  preferably 
of  hard  wood,  having  a  slight  taper.  This  taper  should  vary  with 
the-  span  of  the  arch,  the  longer  the  span  the  less  the  taper.  To 
lower  the  centres  equally  the  wedges  should  be  driven  back  uni- 
formly. To  facilitate  this,  compound  wedges  are  sometimes 
used.  By  driving  the  wedge  all  work  resting  on  the  wedge  will 
be  lowered  uniformly. 

[269] 


Handbook  for  Cement  and  Concrete  Users 

Sand  boxes  usually  consist  of  a  steel  cylinder  in  which  sand  is 
confined.  A  wooden  plunger  rests  on  the  sand,  and  on  these  wooden 
plungers  is  carried  the  centring  of  the  arch.  Near  the  bottom  of 
the  cylinder  is  a  plug  which  may  be  withdrawn  and  replaced  at 
pleasure,  by  means  of  which  the  outflow  of  the  sand  is  regulated. 
As  the  sand  is  allowed  to  escape,  the  centres  will  lower  and  the 
amount  of  this  lowering  can  be  easily  controlled  by  the  amount  of 
sand  allowed  to  escape.  In  using  sand  boxes  particular  care  should 
be  exercised  first  to  secure  a  proper  sand,  and  second  to  exclude  all 


Cn>ss  Stringer 


FIG.  92. — End  View  of  Centre  for  Short  Elliptical  Arch  Spans. 

foreign  material  from  the  boxes,  which  must  also  be  properly  sealed. 
Where  any  of  these  precautions  are  lacking  trouble  is  likely  to  be 
experienced  either  through  the  sand  flowing  prematurely,  or  its 
failure  to  flow  at  the  proper  time. 

The  type  of  centres  to  be  used  in  any  case  will  depend  entirely 
upon  local  conditions.  Where  it  is  desirable  to  obstruct  the  opening 
as  little  as  possible,  the  trussed  form  of  centring  would  probably  be 
best  adapted. 

In  other  cases  where  the  restriction  of  the  opening  is  of  little  or 
no  importance,  bents  would  probably  be  the  most  economical  and 
satisfactory. 

[270] 


Concrete  Arches  and  Arched  Bridges 


Concreting  the  Arch. — For  convenience  in  concreting,  an  arch 
is  frequently  divided  into  a  number  of  strips,  which  are  practically 
arches  in  themselves.  In  all  cases  the  concreting  should  be  carried 
up  from  the  springing  line  toward  the  crown,  uniformly  on  each 
side  of  the  arch.  While  this  concreting  is  in  progress  the  action  of 
the  centres  should  be  carefully  observed.  Generally  as  the  load  on 
the  haunch  increases,  the  crown  will  tend  to  rise.  If  this  tendency 
becomes  excessive,  it  may  be  overcome  by  loading  the  crown  with 
any  material  that  is  convenient,  or  by  placing  the  concrete  for  that 


foot  Blocks.  &&*%/> 

El-o   NEWS. 


P~~I  tlova-ri 

FIG.  93. — Travelling  Form  for  Roof  Arch,  New  York  Subway  Tunnels. 


portion  of  the  arch  before  proceeding  further  with  the  haunches. 
It  is  well,  if  this  method  of  placing  the  concrete  is  used,  to  so  divide 
the  arch  that  a  complete  ring  .may  be  placed  without  intermis- 
sion. 

Another  method  is  to  divide  the  arch  in  strips  extending  the  full 
width  of  the  arch.  The  strips  are  first  placed  near  the  springing 
line,  then,  to  overcome  the  tendency  of  the  crown  to  rise,  the  strip 
at  the  crown  is  placed  and  so  on  until  the  arch  is  completed. 

Backfilling. — Backfilling  is  usually  begun  after  the  arch  has 
hardened  but  before  the  centres  are  struck.  The  reason  for  this 
is  obvious.  If  the  filling  were  placed  after  the  removal  of  the 
centres,  it  would  be  necessary  to  place  the  filling  uniformly  over  the 

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Handbook  for  Cement  and  Concrete  Users 

arch,  as  filling  a  large  weight  on  one  side  while  the  other  is  unloaded 
might  so  seriously  deform  an  arch  as  to  endanger  its  safety. 

On  the  other  hand,  when  parapet  wall  and  railing  are  built 
before  the  centres  are  removed,  the  settlement  of  the  arch  may 
cause  these  to  crack  badly,  and  while  this  would  in  no  way  endanger 
the  safety  of  the  arch,  still  it  is  unsightly  and  therefore  to  be  avoided. 
It  would  therefore  appear  that  in  some  cases,  particularly,  where, 
instead  of  earth  backfill,  a  system  of  relieving  arches,  etc.,  are  used, 
that  when  possible  the  centres  should  be  removed  and  the  arch 
allowed  to  settle  in  place  before  that  portion  of  the  work  above 
the  arches  is  begun. 

A  properly  designed  and  executed  concrete  or  reinforced  arch, 
is  economical,  permanent,  strong,  rigid,  and  last  but  not  least,  can 
easily  be  made  a  thing  of  beauty.  Various  concrete  arch  bridges 
have  been  built  where  the  effect  is  as  pleasing  as  the  best  stone 
arches,  and  at  a  considerable  saving  in  cost.  Also  the  introduction 
of  reinforced,  concrete  permits  of  a  light,  graceful  arch  being  built 
which  is  not  attainable  in  stone  masonry. 


[272] 


CHAPTER  XXIV 

CONCRETE    BEAM    AND    GIRDER    BRIDGES 

Advantages  of  Concrete  Bridges. — Kinds  of  Girder  Bridges. — Reinforced-Concrete 
Trusses. — Viaducts.  —  Concrete  Floors.  —  Abutments. — Centring. — Depositing 
Concrete. — Surface  Finish. 

Advantages  of  Concrete  in  Bridge  Work. — The  use  of  concrete 
in  bridges  was,  until  quite  recently,  limited  to  the  arch.  This 
limitation  was  caused  by  the  low  tensile  strength  of  concrete,  and 
where,  for  any  reasons,  the  arch  was  considered  undesirable,  the 
use  of  steel  or  timber  became  necessary.  With  the  introduction  of 
reinforced  concrete,  however,  the  limitation  of  concrete  work  ceased 
to  exist,  as  by  the  proper  placing  of  steel  reinforcement,  the  concrete 
could  be  relieved  of  all  tensile  stresses,  and  at  the  same  time  its  great 
compressive  strength  called  into  play.  We,  therefore,  at  the  present 
time,  find  not  only  arches  of  reinforced  concrete,  but  also  various 
types  of  flat  bridges,  and  in  a  few  cases  even  trusses  constructed  of 
this  reliable  material. 

Bridges,  of  all  engineering  structures,  are  probably  the  most 
exposed  to  the  action  of  external  destructive  forces,  and  at  the  same 
time  receive  the  severest  load  treatment. 

In  bridges  of  steel  or  wood,  constant  inspection,  painting,  and 
repairing  are  necessary  if  the  structure  is  to  be  kept  in  anything  like 
first-class  condition,  and  even  when  these  are  carried  on,  almost 
continually,  periodic  renewals  will  be  necessary.  This  causes  the 
cost  of  maintenance  to  be  very  high,  and  this  cost  of  maintenance 
is  a  large  and  important  factor  in  the  final  cost  of  the  bridge. 

With  concrete  bridges  this  continual  painting  and  repairing  is 
entirely  unnecessary  and  the  cost  of  maintenance  is  therefore  very 
small.  Also  as  concrete  increases  in  strength  with  age,  and  as  it  is 
in  no  way  affected  by  atmospheric  conditions,  a  well  designed  and 
constructed  concrete  bridge  may  be  said  to  be  everlasting.  A 
18  [273] 


Handbook  for  Cement  and  Concrete  Users 

concrete  bridge,  therefore,  when  once  built  is  built  for  all  time,  and 
periodic  renewals  are  entirely  obviated. 

The  initial  cost  of  a  concrete  bridge  is  therefore  practically  its 
final  cost.  It  would  appear,  moreover,  that  even  should  the  first 
cost  of  a  concrete  bridge  be  considerably  higher  than  the  initial 
cost  of  a  steel  or  timber  structure,  that  in  view  of  its  extremely  long 
life  and  very  low  cost  of  maintenance,  a  concrete  bridge  would  be 
the  most  economical  in  the  end. 

The  initial  cost  of  a  concrete  bridge,  while  somewhat  greater 
than  that  of  a  timber  structure,  is  frequently  lower  than  the  first  cost 
of  a  steel  bridge.  In  localities  where  suitable  sand,  gravel,  and 
broken  stone  are  easily  available,  necessitating  the  transportation 
of  only  a  comparatively  small  amount  of  cement,  and  reinforcing 
steel,  the  initial  cost  of  a  concrete  bridge  will  be  considerably  less 
than  that  of  a  steel  bridge,  and  will  approach  very  closely  the  first 
cost  of  a  timber  structure. 

Another  advantage  of  concrete  bridges  is  that  the  major  portion 
of  the  work  can  be  readily  done  by  local  labor,  and  a  great  portion 
of  the  material  can  be  purchased  locally.  Thus  a  large  percentage 
of  the  money  spent  in  the  construction  remains  in  the  community, 
and  the  community  is  therefore  doubly  benefited. 

Traffic  passing  over  a  concrete  bridge  makes  little  or  no  noise. 
The  same  amount  of  traffic  passing  over  a  steel  or  timber  bridge 
would  cause  a  noise  that  would  be  heard  for  a  considerable  distance. 
This  is  particularly  true  where  either  steam  or  electric  cars  form 
part  of  the  traffic.  This  elimination  of  all  noise  is  particularly 
desirable  in  built-up  communities,  such  as  cities  and  large  towns. 

Concrete,  before  'it  has  set,  is  extremely  plastic,  and  can  there- 
fore be  moulded  into  practically  any  shape  or  form  desired.  Thus 
in  building  a  bridge  of  concrete,  a  very  pleasing  and  artistic  design 
may  be  executed,  at  but  a  small  increase  of  cost,  resulting  in  an 
efficient  and  beautiful  bridge.  With  but  few  exceptions  steel 
bridges  are  far  from  being  things  of  beauty,  and  at  their  best,  can  in 
no  way  compare  with  concrete  structures. 

Classes  of  Concrete  Bridges. — Concrete  bridges  may  be  classified 
as  either  arch  bridges  or  flat  bridges.  Arch  bridges  of  both  plain 
and  reinforced  concrete  have  been  discussed  in  the  preceding  chapter. 
A  flat  bridge  is  one  in  which  the  load  on  the  structure  acts  vertically 

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Concrete  Beam  and  Girder  Bridges 

on  the  supports.  A  flat  bridge  may  consist  of  either  a  straight  flat 
slab,  or  of  a  combination  of  beams  and  slabs  or  of  a  combination  of 
beams,  girders,  and  slabs.  All  flat  bridges  require  reinforcement. 

Flat- Slab  Bridges. — The  simplest  form  of  a  reinforced -concrete 
bridge  is  the  flat  slab.  This  consists  ofta  sheet  of  concrete  of 
uniform  thickness,  supported  at  each  end.  It  is  designed  as  a  slab 
whose  span  is  the  distance  between  the  abutments.  The  main 
reinforcement,  therefore,  extends  from  abutment  to  abutment,  and 
may  be  of  any  of  the  numerous  forms  of  reinforcing  bars  common 
to  reinforced  concrete.  Structural  shapes  and  even  old  railroad 
rails  have  been  used  in  this  capacity,  and  have  given  complete 
satisfaction. 

A  secondary  reinforcement  perpendicular  to  the  longitudinal 
bars  or  shapes  should  be  placed  in  all  bridges  of  this  type.  The 
function  of  this  secondary  reinforcement  is  to  aid  in  the  distribution 
of  stresses  due  to  concentration,  to  take  temperature  stresses,  and 
to  prevent  the  formation  of  cracks.  Generally  no  special  pro- 
visions for  shear  are  necessary  in  flat  slabs.  It  is  customary, 
however,  to  bend  a  portion  of  the  main  reinforcement  up  to  the 
top  of  the  slab  near  the  point  of  support.  Should  the  bridge  be 
continuous  over  two  or  more  spans,  additional  reinforcement  should 
be  placed  at  the  top  of  the  slab,  over  the  points  of  support,  to  take 
the  tensile  stresses  caused  by  the  negative  bending-moment. 

Bridges  of  this  type  will  generally  be  found  economical  for 
spans  up  to  15  feet.  For  larger  spans  the  thickness  of  the  slab  and, 
hence  the  dead  load,  becomes  excessive,  and  some  other  type  of 
bridge  should  be  used. 

Beam-and-Slab  Bridges. — Beam-and-slab  bridges  consist  of  two 
or  more  reinforced-concrete  beams  extending  from  abutments 
to  abutments  and  supporting  a  slab  on  which  the  roadway  is  laid. 
These  beams  are  in  the  majority  of  cases  entirely  below  the  slab, 
but  in  some  instances  are  carried  up  above  the  slab  to  form  the  side 
rail. 

The  design  of  a  beam-and-slab  bridge  is  essentially  the  same  as 
that  of  a  slab  and  beam  in  ordinary  floor  construction.  The  slab 
is  supported  by  the  beams  and  carries  the  superimposed  live  and 
dead  loads.  The  beams  are  supported  by  the  abutments  and  carry 
the  slab  with  its  attendant  live  load.  The  beams  must  be  carefully 

[275] 


Handbook  for  Cement  and  Concrete  Users 

investigated  for  shear  and  where  necessary  for  this  purpose  additional 
reinforcement  should  be  introduced. 

Where  the  beams  are  entirely  below  the  slab  they  may  be  con- 
sidered as  T-beams  and  designed  as  such.  In  this  case  the  slab 
and  floor  beams  should  be  poured  at  the  same  time  so  as  to  assure 
a  proper  bonding  of  the  slab  and  beam. 

Bridges  of  this  type,  on  account  of  their  low  cost  and  light  weight, 
are  particularly  adapted  to  light  highway  bridges,  etc.,  and  are 
economical  in  general  for  spans  up  to  20  feet. 

Girder  Bridges. — Girder  bridges  are  usually  composed  of  two 
or  more  large  reinforced-concrete  girders  supporting  intermediate 
beams,  which  in  turn  carry  the  slab  on  which  the  roadway  is  laid. 

In  designing  a  girder  bridge,  the  slabs  are  designed  to  carry  the 
superimposed  loads  to  the  beams.  The  beams  are  designed  to 


V  i 

Fro.  94. — Typical  Reinforced-Concrete  Girder  Bridge. 

carry  the  loads  to  the  girders,  and  the  girders  are  designed  to  carry 
the  loads  to  the  abutments.  Both  the  beams  and  the  girders  should 
be  carefully  investigated  for  shear  and  where  necessary  reinforcing 
for  this  purpose  should  be  introduced.  The  girder  should  also  be 
carefully  investigated  to  see  that  sufficient  compressive  strength  is 
obtained  in  their  upper  portion.  Steel  for  temperature  stresses  and 
to  prevent  cracking  should  be  placed  where  necessary  throughout 
the  structure. 

Girder  bridges  have  been  constructed  with  spans  as  great  as 
TOO  feet.  They  are  not,  however,  economical  for  such  long  spans 
and  should  be  used  for  these  only  where  the  restriction  of  the  water- 
*  way  or  poor  foundations  make  the  arch  inadvisable. 

In  some  girder  bridges  the  girders  have  been  designed  as  canti- 
levers at  the  points  of  supports,  and  carrying  a  simple  span  at  the 

[276] 


Concrete  Beam  and  Girder  Bridges 

centre.  In  such  cases  the  girders  are  deepest  at  the  abutment,  and 
have  somewhat  the  appearance  of  an  arched  rib.  The  position  of 
the  reinforcement  is,  however,  radically  different.  If  some  of  the 
very  flat  arches  had  been  designed  thus  instead  of  as  arches,  the 
unsightly  cracks  over  the  haunches  so  common  to  them  would 
probably  have  been  avoided. 

Reinforced-Concrete  Trusses. — A  true  truss  of  reinforced  concrete 
was  constructed  by  Considere  in  France.  The  compression  mem- 
bers were  of  concrete  reinforced  by  spiral  hooping  as  in  a  hooped 
column.  The  tension  members  were  of  steel  surrounded  by  concrete. 
This  bridge  was  built  only  as  a  test  of  the  strength  of  the  hooped 
member  and  when  finished  was  loaded  until  failure  took  place.  It 
demonstrated,  however,  that  bridges  of  this  type  may  be  built  in 
reinforced  concrete.  The  economy  of  such  a  bridge  is  doubtful, 
as  the  cost  of  form  work  must  have  been  excessive. 

Girder  bridges  are  occasionally  constructed  with  open  webs. 
The  girder  is  thus  given  the  appearance  of  a  truss.  Beyond  the 
saving  of  a  little  weight,  this  type  of  bridge  has  no  advantage  over 
a  bridge  with  a  solid  girder,  and  as  anything  approaching  an  exact 
determination  of  the  stress  acting  in  the  open  girder  is  impossible, 
they  should  be  avoided. 

Concrete  Floors  for  Steel  Bridges. — In  long- span  highway 
bridges,  when  steel  trusses,  are  necessary,  the  wood  planking,  which 
until  recently  was  the  standard  flooring,  is  now  being  largely  re- 
placed by  reinforced-concrete  slabs,  supported  on  the  steel  beams. 
On  these  slabs  the  wearing  surface  of  the  roadway  is  placed.  A 
floor  of  this  type  is  more  expensive  in-  first  cost  than  a  plank  floor, 
but  it  will  outlast  the  bridge  itself,  while  a  wood  floor  requires  re- 
newing in  from  one  to  five  years. 

In  steel  railroad  bridges,  reinforced-concrete  floors  are  now 
being  extensively  used  to  replace  trough  and  open  floors.  These 
reinforced-concrete  floors  are  practically  noiseless,  and  may  be 
ballasted  in  the  same  way  as  the  rest  of  the  roadway,  thus  making 
a  uniform  roadbed  throughout  the  line. 

Reinforced  concrete  may  also  be  used  to  strengthen  existing 
steel  bridges  when  same  have  become  insufficient  for  the  present 
need,  or  so  badly  corroded  as  to  be  considered  dangerous.  In  the 
bridge  at  Perigueux,  France,  the  lattice  bars  of  the  main  girders 

[277] 


Handbook  for  Cement  and  Concrete  Users 

and  the  webs  of  the  cross  beams  were  so  badly  corroded  by  the  gases 
from  locomotives  stopping  under  them  that  the  safety  of  the  bridge 
was  threatened.  The  bridge  was  protected  and  strengthened  by 
incasing  all  the  old  steel  members  in  reinforced  concrete,  and  a 
new  reinforced-concrete  floor  was  then  built.  This  resulted  in  a 
new  bridge,  stronger  and  stiffer  than  the  old  one,  that  would  not  be 
acted  upon  by  the  gases  from  the  locomotives.  If  it  had  been 
necessary,  the  strength  of  the  bridge  could  have  been  still  further 
increased  by  the  addition  of  reinforcing  rods  parallel  to  and  along- 
side of  the  beams  and  girders. 

Abutments. — The  abutments  of  a  concrete  bridge  may  be 
constructed  in  either  plain  or  reinforced  concrete.  They  should 
be  designed  to  resist  overturning  due  to  the  pressure  of  the  earth 
backing,  and  at  the  same  time  to  so  distribute  the  load  on  the 
foundation  caused  by  this  pressure,  and  the  load  of  the  bridge,  that 
in  no  place  will  the  load  on  the  soil  exceed  its  safe  bearing  value. 
In  some  cases  the  bridge  is  rigidly  attached  to  the  abutments  while 
in  others  it  simply  rests  in  the  seat.  In  the  first  case  all  tendency 
of  the  bridge  to  expand  or  contract,  due  to  temperature  stresses,  must 
be  resisted  by  the  abutments  or  internally  by  the  bridge  itself.  In 
the  second  case  the  bridge  slides  on  its  seat  as  this  expansion  or 
shortening  takes  place.  For  long  bridges  the  second  method  is 
preferable  while  for  short  bridges  either  method  will  give  satisfactory 
results. 

Centring. — The  form  work  for  flat  reinforced-concrete  bridges 
is  essentially  the  same  as  for  floor  construction.  Troughs  are 
formed  in  the  centring  to  receive  the  beams  and  girders  when  they 
extend  below  the  slab,  and  when  the  girders  or  beams  are  above, 
the  slab  formwork  is  built  up  to  receive  them.  The  formwork 
should  be  as  firm  and  unyielding  as  possible,  so  that  there  will  be 
no  deflection  or  distortion  when  the  concrete  is  placed.  It  should 
also  be  sufficiently  tight  to  prevent  the  cement  and  water  from  leaking 
out,  thereby  causing  a  poor  porous  concrete. 

Depositing  Concrete. — In  general  the  concrete  should  be  de- 
posited as  quickly  as  possible  so  as  to  insure  a  monolithic  structure. 
Beams,  girders,  and  slabs  should,  if  possible,  be  deposited  at  the 
same  time,  especially  where  the  beams  have  been  designed  as  T- 
beams.  Where  the  beams  or  girders  are  deep,  it  is  sometimes  in- 

[278] 


Concrete  Beam  and  Girder  Bridges 


advisable  to  do  this,  as  the  contraction  of  the  beam  or  girder  in 
setting  may  cause  it  to  crack  away  from  the  slab.  In  such  cases  it 
would  be  well  to  concrete  the  beam  or  girder  first,  and  the  slab  after 
a  sufficient  interval  had  elapsed.  In  this  case,  however,  if  T-action 
is  desired,  special  reinforcement  will  be  necessary  to  bond  the  beam 
and  the  slab  properly  together. 

Finish. — In  some  structures,  where  appearance  is  of  little  im- 
portance, the  concrete  can  be  left  just  as  it  comes  from  the  moulds, 
and  if  sufficient  care  has  been  taken  in  building  the  form  work  and 
placing  the  concrete,  a  very  satisfactory  finish  will  result.  A  better 
finish  may  be  obtained  by  placing  against  the  forms  a  one-inch  coat- 

TABLE   XXV. — PRINCIPAL    DIMENSIONS    AND    QUANTITIES    OF 
MATERIALS  FOR  SLAB  BRIDGES. 

(From  "Concrete  in  High  way  Construction,"  published  by  Atlas  Portland  Cement  Co.) 


i 

5 

LONGITUDINAL 
BARS. 

ABUTMENT 
WALLS. 

LENGTH  OF 
SIDE  WALLS. 
FEET. 

Cu.  YDS.  OF 
CONCRETE. 

POUNDS  OF 
STEEL  RODS. 

°l 

i 

TO    O 

*jL 

8d  • 

L 

*°  ^tn 

01 

J1"1 

T^     CH 

_o  "" 

_N    £"S 

Is! 

11 

'S  °  c 

6  Ft.* 

8  Ft.* 

6  Ft.* 

8  Ft.* 

6  Ft.* 

8  Ft.* 

(J 

P 

s 

Q  "^ 

P 

^fcM 

8 

9 

. 

6 

8 

20 

32.0 

38.0 

43 

53 

2715 

3440 

10 

ir 

f 

5 

1  1 

23 

34-5 

40.5 

49 

60 

3195 

3880 

12 

13 

^ 

5 

13 

27 

37-0 

43-0 

57 

69 

3420 

4100 

16 

IS 

4 

5 

15 

45 

41-5 

47-5 

73 

87 

4375 

5035 

ing  of  cement  mortar  and  then  placing  the  concrete  behind  it. 
This  mortar  may  be  applied  with  a  trowel  or  behind  a  steel  plate 
which  separates  it  from  the  concrete  backing. 

In  the  removal  of  forms  this  facing  may  be  treated  in  various 
ways  as  described  in  Chapter  XII.  If  the  mortar  is  not  set  too 
hard,  it  may  simply  be  brushed  with  a  stiff  wire  brush  and  water. 
This  will  remove  the  outer  film  of  cement  and  bring  the  grains  of 
sand  into  prominence.  If  the  mortar  is  set  too  hard  to  be  acted 
upon  by  the  wire  brush,  sand  or  a  cement  block  may  be  used  and  the 
same  effect  attained.  By  a  proper  selection  of  the  sand,  various 
color  effects  may  be  obtained  in  this  way. 


*  Distance  in  feet  from  top  of  footing  course  to  bottom  of  slab. 

[279] 


Handbook  for  Cement  and  Concrete  Users 

If  a  mortar  facing  is  not  desired,  the  concrete  itself  may  be 
rubbed,  sanded,  or  tooled  until  the  outer  film  of  cement  is  removed 
and  the  aggregate  exposed.  Where  proper  thought  has  been  given 
to  the  selection  of  the  aggregate,  very  pleasing  effects  may  be  ob- 
tained in  this  manner. 

If  further  treatment  is  thought  advisable,  the  surface  of  the 
concrete  may  be  washed  with  a  weak  solution  of  acid.  After  the 
acid  wash  it  is  well  to  again  wash  it  with  an  alkaline  solution  to 
neutralize  any  acid  that  may  remain  in  the  concrete. 


[280] 


SECTION  V 

THE  USES  OF  CONCRETE  FOR 
SPECIAL  PURPOSES 


CHAPTER  XXV 

CONCRETE   IN    SEWERAGE    AND   DRAINAGE 
WORKS 

Advantages  of  Concrete  for  Sewers. — Forms  of  Sewers. — Combined  and  Separate 
Systems. — Dimensions  of  Sewers. — Construction  of  Sewers  and  Conduits. — Quan- 
tity of  Flow. — Culverts  and  Drains. — Types  of  Culverts. — Imperviousness  of 
Sewers  and  Conduits. — Tables  of  Dimensions  for  Culverts. 

Advantages  of  Concrete  for  Sewers. — In  no  situation  perhaps 
are  constructive  materials  subjected  to  greater  destructive  forces 
than  in  subsurface  work,  particularly  where  the  ground  is  charged 
with  corrosive  chemical  and  electrical  influences.  Under  such 
conditions,  many  sewers  and  water-carrying  conduits  built  of  iron 
and  steel  have  been  destroyed  in  the  course  of  comparatively  few 
years.  It  is  therefore  with  reason  that  municipal  engineers 
throughout  the  country  rejoice  that  in  concrete,  both  plain  and  rein- 
forced, a  material  has  been  found  that  will  not  only  be  cheaper  than 
brick  or  masonry  but  more  enduring  than  steel  and  iron  and  more 
susceptible  to  use  under  any  condition  from  the  largest  conduit  to 
the  smallest  pipe. 

While  in  Europe,  factory-made  cement  pipe  has  been  largely 
used  up  to  7  feet  in  diameter,  American  engineers  have  found  it 
more  economical  up  to  the  present  time  to  mould  all  pipes  and 
sewers  exceeding  3  feet  in  diameter  right  in  place.  For  pipes  smaller 
than  3  feet,  difficulty  in  securing  and  using  adequate  forms  have 
made  it  advisable  to  manufacture  them  in  factories  specially  equipped 
for  turning  them  out  in  large  quantities  and  standard  sizes. 

[28l] 


Handbook  for  Cement  and  Concrete  Users 

The  economy  in  the  manufacture  of  the  smaller  sizes  arises 
from  the  fact  that  the  specially  moulded  pipes  have  very  much 
thinner  shells,  6  inches  being  about  the  thinnest  that  can  be  moulded 
on  the  job,  while  the  manufactured  pipe  runs  from  1/2  to  3  1/2 
inches  thick.  There  is  thus  a  large  saving  of  material,  but  this 
economy  disappears  when  sizes  larger  than  3  or  4  feet  are  reached. 
A  well-constructed  concrete  pipe  will  give  as  good  results  as  a  vitrified 
clay  pipe  and  be  less  costly  than  the  latter. 

The  process  of  making  these  pipes  has  already  been  described 
in  the  chapter  on  concrete  products. 

Another  advantage  in  the  use  of  concrete  for  sewer  work  is  the 
smooth  surface  obtainable,  and  smoothness  of  surface  is  very  de- 
sirable to  reduce  the  frictional  resistance  of  the  flowing  sewerage. 

Systems  of  Sewerage. — Sewers  are  built  in  circular,  egg-shaped, 
and  other  forms,  depending  upon  the  relative  quantity  to  be  carried 
during  low  and  high  stages  of  flow,  and  upon  whether  the  rain  or 
storm  water  is  to  be  carried  in  the  same  system  as  the  sewerage 
proper.  This  is  a  very  important  question  and  is  usually  one  of 
the  first  things  to  be  decided  upon  in  any  extensive  sewer  project. 
When  the  storm  water  and  sewage  are  carried  in  the  same  set  of 
sewers,  we  have  a  " combined"  system.  Separate  sewers  for  the 
storm  water  and  for  the  sewage  proper  is  referred  to  as  the  ''separ- 
ate" system. 

While  for  a  detailed  discussion  of  the  merits  of  each  system,  the 
reader  must  be  referred  to  special  works  on  sewerage,  a  few  remarks 
on  the  controlling  features  may  not  be  out  of  place. 

Separate  and  Combined  Systems. — The  separate  system  is 
employed  principally  when  the  sewage  must  receive  some  purifica- 
tion treatment  before  being  discharged  into  streams.  In  such  cases 
the  storm  water  is  excluded  to  reduce  the  maintenance  charge  at 
the  disposal  plant.  Where  the  sewage  discharges  directly  into 
running  water  without  preliminary  treatment,  the  combined  system 
is  to  be  preferred,  as  the  storm  water  acts  as  a  cleansing  agent  and 
but  little  artificial  flushing  is  required. 

Forms  of  Sewers. — The  circular  sewer  is  built  wherever  con- 
ditions permit  its  use,  as  with  a  given  external  area  the  circular 
section  requires  less  material  than  any  other  form,  and  is  thus  the 
most  economical.  Where,  however,  the  amount  of  sewage  fluctu- 

[282] 
.  .V  1 


Concrete  in  Sewerage  and  Drainage  Works 

ates  largely,  the  circular  section  offers  greater  frictional  resistance 
to  flow  at  low  stages  and  the  egg-shaped  section  is  employed.  The 
increased  frictional  resistance  to  flow  in  the  circular  section  arises 
from  the  fact  that  a  greater  area  of  surface  is  covered  for  the  same 
quantity  of  flow  than  in  the  case  of  the  narrower  egg-shaped  section. 
In  the  latter  the  dimensions  are  so  fixed  that  a  fairly  uniform  rate 
of  flow  is  obtained  under  all  conditions  of  flow,  and,  as  in  the  com- 
bined system  the  flow  is  sometimes  very  large,  and  sometimes  very 
slight,  the  egg-shape  is  very  well  adapted. 

Many  horseshoe-shaped  conduits  and  sewers  have  been  con- 
structed, this  shape  being  usually  easier  to  build,  particularly  when 
made  of  brick;  but  with  the  introduction  of  concrete  and  improve- 
ment in  collapsible  forms,  the  circular  section  is  the  predominating 
type.  The  horseshoe  section  is,  however,  employed  in  very  large 
conduits  for  water  supply  where  the  flow  is  fairly  uniform  and  the 
greater  frictional  losses  and  the  extra  material  required,  being 
counterbalanced  by  the  greater  ease  of  construction. 

Depth  of  Flow. — Sewers  and  conduits  not  flowing  under  pressure 
reach  their  maximum  capacity  when  flowing  about  0.9  full,  the 
flow  being  greater  at  this  depth  than  when  the  whole  section  is  filled, 
owing  to  the  increased  surface  friction  at  the  top  and  the  consequent 
reduction  in  velocity. 

Velocity  in  Sewers. — The  velocity  in  sewers  is  kept  within  the 
limits  of  2  1/2  to  10  feet  per  second  and  the  grades  so  established 
that  velocities  between  these  limits  are  obtained.  The  lower 
velocity  is  necessary  to  prevent  the  deposit  of  solid  matter  in  suspen- 
sion and  the  higher  velocity  to  prevent  excessive  wear  on  the  material 
composing  the  surface  of  the  conduit,  as  the  abrasive  power  of  water 
flowing  at  high  velocities  is  very  great.  It  is  partly  for  this  reason 
that  conduits  under  pressure  where  the  water  moves  at  a  high  velo- 
city are  generally  built  of  steel  or  iron,  the  further  reason  being  that 
the  high  pressure  exerted  on  the  walls  would  be  fatal  to  ordinary 
masonry.  Reinforced  concrete,  however,  has  now  come  into  favor 
even  in  high-pressure  conduits,  and  many  of  the  tunnels  of  this 
character  are  being  designed  on  the  new  Catskill .  waterworks  for 
the  City  of  New  York. 

Dimensions  of  Sewers.— The  size  of  the  sewer  or  conduit  is 
fixed  by  the  amount  of  material  to  be  carried  and  the  grades  ob- 

[283] 


Handbook  for  Cement  and  Concrete  Users 

tainable;   the  smallest  size  consistent  with  the  limiting  velocities  is 
usually  adopted. 

The  size  and  the  shape  having  been  determined,  the  thickness  of 
the  top,  sides,  and  bottom  are  to  be  fixed.  There  is  no  special 
method  or  formula  for  proportioning  these  parts  as  the  conditions 
are  so  variable.  The  depth  below  the  surface,  the  character  of  the 
material,  the  foundation,  etc.,  must  be  considered.  Experience 
has,  however,  fixed  certain  standard  dimensions  which  may  safely 
be  employed  for  various  sizes  both  in  plain  and  reinforced-concrete 


FIG.  95.  —  Standard  Section  in  Plain  Concrete.     New  York  Rapid  Transit  System. 

sewers,  and  these  are  given  below.  It  will  be  noticed  that  these 
dimensions  point  to  a  very  simple  rule  for  finding  the  thickness  at 
the  crown  of  circular  sewers;  i.e.,  the  thickness  at  the  crown  in 
inches  is  equal  to  the  number  of  feet  in  diameter  +  i,  the  minimum 
thickness  being  4  inches. 

The  amount  of  steel  in  reinforced-concrete  sewers  and  conduits 
must  be  sufficient  to  take  care  of  the  bursting  strain  due  to  the 
hydrostatic  pressure  of  the  water  or  sewage.  This  quantity  may  be 
determined  by  the  simple  formula: 


of  steel. 


[284] 


Concrete  in  Sewerage  and  Drainage  Works 


p  =  Internal  hydrostatic  pressure  in  Ibs.  per  sq.  in. 

d  =  Internal  diameter  in  inches. 

/  =  Allowable  working  stress,  for  steel,  in  Ibs.  per  sq.  in. 


Jlo" 


/<*-£) 


C/r. 


6".    . 


!  S" ,. 


T"  •'  .. 


/o 


•ML 


FIG.  96.— Standard  Sections:   Reinforced  Concrete  Sewers.     New  York  Rapid 
Transit  System. 

A  =  Area  of  steel  required  for  each  longitudinal  foot  of  con- 
crete. 

[285] 


Handbook  for  Cement  and  Concrete  Users 

Construction  of  Sewers. — The  construction  of  sewers  follows 
the  general  methods  already  described  in  mixing  and  placing 
concrete.  The  special  features  that  accompany  sewer  work  are: 

1.  The  construction  of  the  trenches  to  the  proper  depth.     These 
should  be  somewhat  wider  than  the  actual  width  of  the  masonry, 
to  allow  working  room,  the  excess  being  later  carefully  backfilled. 

2.  The  trenches  must  be  adequately  braced  so  that  no  sliding 
of  material  will  occur  during  the  progress  of  the  work.     In  shallow 
cuts  with  a  firm  material  very  little  bracing  is  required,  but  in  soft 
material  heavy  tongue  and  grooved  sheet-piling  is  employed  and 
interlocking  steel  sheet  piling  is  now  coming  into  extensive  use  for 
this  purpose. 

3.  The  bottom   of  the   trench   should   be   properly   prepared; 
loose  and  poor  material  being  removed  and  replaced  by  sand  or  con- 
crete and  the  slope  of  the  bottom  should  be  made  parallel  to  the 
finished  slope  of  the  sewer. 

4.  In  case  the  conduit  or  sewer  is  constructed  in  yielding  soil, 
special  means  must  be  taken  to  secure  good  foundations,  and  for 
this  purpose  piles  are  frequently  driven  and  the  sewer  constructed 
on  a  timber  platform  built  on  these  piles. 

5.  The  excavation  having  been  completed  and  the  foundation 
prepared,  the  concreting  begins;   a  mixture  of  1:3:5  being  suitable 
to  the  heavy  portions  of  the  work  and  a  i :  2 :  4  should  be  employed 
around  the  reinforcement  and  at  the  crown. 

6.  The  forms  for  building  concrete  sewers  may  be  made  of 
wooden  lagging  supported  at  5-  to  6-foot  intervals  by  specially  cut 
timbers  resting  on  posts  or  sills,  or  one  of  the  many  forms  of  collap- 
sible steel  forms  may  be  employed.     These  forms  are  especially 
desirable  where  long  sections  of  sewers  of  uniform  diameter  are  to 
be  built,  as  the  use  and  constant  reuse  of  same  results  in  a  consider- 
able saving  in  form  labor. 

7.  In  laying  concrete  pipe  sewers  having  hubs,  special  excavations 
must  be  made  under  the  joints  of  the  pipes  to  provide  room  for  the 
enlarged  ends,  and  particular  care  should  be  taken  that  the  pipes 
are  properly  bedded,  as  any  unevenness  in  the  bed  may  result  in 
open  joints  and  broken  pipes. 

8.  After  the  concrete  has  been  deposited  and  has  hardened,  the 
forms  are  removed  to  be  used  over  again,  and  sections  of  the  com- 

[286] 


Concrete  in  Sewerage  and  Drainage  Works 


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[287] 


Handbook  for  Cement  and  Concrete  Users 

pleted  sewer  are  backfilled  uniformly  from  both  sides  so  as  to 
eliminate  eccentric  strains  on  the  roof.  In  placing  the  backfilling, 
care  should  be  taken  that  no  heavy  stones  are  poured  or  rammed 
against  the  completed  sewer  concrete  that  would  be  likely  to 
injure  it. 

Sewers  and  conduits  are  frequently  constructed  in  tunnels  where 
the  concrete  work  must  necessarily  be  done  under  trying  conditions. 
The  construction  of  tunnels  is  perhaps  the  most  difficult  of  all 
engineering  undertakings  and  the  accomplishments  in  this  field 
during  the  last  twenty-five  years  have  been  marvelous  in  the  ex- 
treme. This  is  particularly  the  case  in  subaqueous  work  where 
life  and  limb  are  in  constant  danger  both  from  the  threatening 
waters  on  the  outside  and  the  air  on  the  inside,  which  is  highly 
compressed  to  keep  the  water  out. 

Under  the  cramped  and  difficult  conditions  met  with  in  tunnel 
work,  the  placing  of  the  concrete  is  slow,  and  special  forms  of 
mixers  and  conveyors  are  frequently  employed  to  accomplish  it. 
It  is,  however,  here  that  cement  finds  a  large  field  of  usefulness  in 
other  ways  than  mere  concrete-placing,  for  after  the  concrete  has 
been  placed,  there  remain  numerous  crevices,  and  holes  near  the 
roof  of  the  tunnel  which  can  not  be  filled  up  in  the  ordinary  way  and 
here  liquid  concrete  or  grout  is  employed  and  pumped  in  under 
high  pressure  as  described  in  Chapter  XXXI. 

Quantity  of  Flow  in  Sewers. — In  the  "separate"  system  the 
amount  of  sewage  to  be  taken  care  of  is  equal  to  the  water  supply, 
as  it  is  figured  that  the  entire  water  supply  sooner  or  later  will  reach 
the  sewer.  This  amount  in  any  extensive  system  is  taken  generally 
as  100  gallons  per  day  per  head  of  population  tributary  to  the  sewer. 
This  total  quantity  is  proportioned  irregularly  throughout  the  day, 
the  maximum  flow  being  possibly  10  gallons  per  person  per  hour. 
This  is  converted  into  its  equivalent  in  cubic  feet  per  second  which 
is  the  unit  of  quantity  in  all  calculations  of  flow. 

The  amount  of  water  reaching  the  sewer  from  storms  is  a  very 
uncertain  quantity  owing  to  the  variability  of  the  factors  involved. 
The  amount  depends  upon: 

1.  The  rate  or  intensity  of  rainfall. 

2.  The  variation  in  rate. 

3.  The  length  or  duration  of  the  rainfall. 

[288] 


Concrete  in  Sewerage  and  Drainage  Works 

4.  The  condition  of  the  surface  particularly  as  regards  its  power 
of  absorption. 

5.  The  slope  of  the  surface. 

6.  The  shape  of  the  surface  and  its  area. 

7.  The  presence  of  obstructions  to  flow,  such  as  vegetation. 

8.  The  proximity  fo  the  sewer  inlets. 

9.  The  carrying  capacity  of  the  sewer. 

A  great  many  studies  have  been  made  to  determine  the  probable 
amount  of  storm  water  for  which  the  sewer  should  be  designed,  but 
no  satisfactory  rule  applicable  to  all  conditions  has  ever  been 
formulated;  the  one  most  commonly  employed  being  the  formula: 

Q  =  C  y  v"  6^ 
in  which 

Q  equals  the  number  of  cubic  feet  reaching  the  •  sewer  per 
second,  for  which  the  conduit  is  designed. 

C  =  a  constant  depending  upon  retentive  power  of  surface. 
3.50  =  for  ordinary  prairie  land. 
5.00  =  for  paved,  rock,  or  frozen  surfaces. 
2.00  =  for  wooded  land. 
y  =  rate  of  rainfall  in  inches  per  hour. 
S  =  slope  of  receiving  surface  in  feet  per  1,000. 
A  =  area  of  receiving  surface  in  acres. 

CULVERTS  AND  DRAINS 

Culverts  are  employed  to  carry  a  stream  or  watercourse  under- 
neath an  embankment  constructed  for  highway,  railroad,  or  other 
purposes.  Drains  are  employed  wherever  the  carrying  off  of 
surplus  water  is  required.  Siphons  are  employed  to  carry  a  stream 
of  water  across  a  hill  or  valley,  the  water  in  such  cases  flowing  under 
pressure.  In  all  these  works,  concrete,  both  plain  and  reinforced, 
is  now  extensively  employed,  brick  work,  iron,  and  steel  being  largely 
abandoned. 

Since  the  purpose  of  culverts  and  drains  is  to  carry  off  surplus 
water  and  thereby  prevent  injury  to  embankments  or  foundations, 
it  is  necessary  to  know  approximately  the  maximum  amount  of 
water  that  may  have  to  be  taken  care  of  during  times  of  extreme 
flood. 

19  [289] 


Handbook  for  Cement  and  Concrete  Users 

There  are  several  ways  in  which  the  required  area  of  a  culvert 
opening  may  be  obtained. 

i st.  The  area  of  the  stream  at  narrow  points  along  the  water- 
course during  freshet  periods  may  be  measured  and  the  required 
area  thus  obtained. 

2d.  The  high  drift  marks  along  the  banks  may  be  examined 
and  the  area  between  the  bed  of  the  stream  and  the  high-water  line 
determined. 

3d.  Culvert  openings  at  other  points  along  the  same  stream 
when  they  have  been  found  ample,  may  be  taken  as  a  safe  guide  to 
proportioning  the  new  culvert. 

4th.  Where  none  of  these  means  for  determining  the  area  of  the 
waterway  can  be  employed,  resort  has  to  be  made  to  some  empirical 
rule  or  formula  which  has  been  established  by  comparing  existing 
culverts  with  the  area  of  land  which  they  drain  or  "drainage  area." 
Perhaps  the  simplest  of  these  is  Myer's  formula: 


Area  in  square  feet  =  \/Drainage  area  in  acres. 

Thus,  for   100  acres  area  required  is   10    sq.  ft.  or  a  3  1/2  foot 
culvert. 

For  900  acres,  30  sq.  ft.  would  be  required  or  a  5  X  6  culvert. 

The  carrying  capacity  is  also,  of  course,  affected  by  the  grade  or 
slope  and  this  is  usually  fixed  by  the  relative  surface  elevations  for 
the  entrance  and  exit.  As  steep  a  slope  as  possible  should  be  given. 

Types  of  Culverts. — The  area  of  waterway  having  been  deter- 
mined, the  type  of  culvert  may  be  selected.  There  are  three  types 
in  general  use,  depending  largely  on  the  area  of  waterway. 

i  st.  The  pipe  culvert  is  available  where  the  area  of  waterway 
does  not  exceed  10  sq.  ft.,  which  requires  a  pipe  36  inches  in  diameter 
or  the  maximum  size  of  concrete  pipe  made.  Manufactured  concrete 
pipes  below  this  size  are  economical  and  very  satisfactory  for  culvert 
construction. 

2d.  Box  culverts  having  rectangular  waterways  are  extensively 
employed  from  the  2'  X  2'  size  up  to  almost  any  size  required. 
They  are  easy  and  cheap  to  build  and  are  employed  for  the  smaller 
sizes  where  shipment  of  ready-made  pipe  is  not  desired,  as  the  box 
culvert  can  be  built  from  materials  and  cements  in  almost  any 
locality. 

290] 


Concrete  in  Sewerage  and  Drainage  Works 

3d.  The  arch  culvert  is  employed  for  the  large  openings  where 
appearance  is  of  more  importance  than  the  question  of  cost,  as  the 
construction  of  arches  is  more  costly  than  plain  rectangular  work. 
In  very  large  culverts,  however,  the  arch  is  somewhat  more  economi- 
cal in  material  for  a  given  area  of  waterway. 

The  larger  culverts,  both  box  and  arch  types,  may  be  reinforced 
and  it  is  good  practice  and  economical  to  do  so,  as  it  enables  much 
lighter  sections  of  concrete  to  be  employed. 

The  concrete  for  culvert  construction  may  be  a  1:3:6  mix,  a 
somewhat  richer  mixture,  however,  being  employed  about  the  rein- 
forcement. Otherwise  the  construction  follows  the  usual  method 


SIT**  I 


7*/r«*«      iacea  to  'b» 


FIG.  98. — Forms  for  Square  Concrete  Culverts. 

of  concrete  work.  The  particular  point  to  be  mentioned  about 
culvert  work  is,  the  protection  of  the  inlet  to  and  outlet  of  the 
waterway  against  any  scour  by  the  flowing  water.  Water  finding 
its  way  underneath  the  floor  or  around  the  ends  will  either  under- 
mine the  culvert  or  erode  the  banks  and  both  of  these  must  be 
prevented.  The  method  of  prevention  consists  in  a  substantial 
stone  or  concrete  pavement  laid  on  the  floor  of  the  culvert  to  con- 
fine the  water  to  its  proper  channel,  and  parapet  walls  to  prevent 
erosion  of  the  embankment. 

The  construction  of  culverts  may  become  a  difficult  matter 
when  a  large  amount  of  water  is  to  be  taken  care  of.  The  best 
method  of  procedure  is  to  excavate  a  temporary  channel  or  provide 

[291] 


Handbook  for  Cement  and  Concrete  Users 

a  temporary  flume  near  the  culvert  site  and  divert  the  course  of 
the  stream  through  the  temporary  waterway.  The  culvert  can 
then  be  constructed  in  the  dry,  and  when  completed,  the  stream 
diverted  into  the  culvert,  the  temporary  channel  being  removed. 

Imperviousness  of  Sewers  and  Conduits. — Sewers,  particularly 
in  the  separate  system,  shoul^  be  as  .impervious  as  it  is  possible  to 
make  them.  There  are  three  important  reasons  for  this,  as: 

i st.  The  necessity  for  excluding  ground  water  from  the  sewer. 
The  infiltration  of  ground  water  is  a  serious  matter  where  the 
sewage  must  be  purified  before  being  disposed  of,  and  records  show 
that  millions  of  gallons  of  ground  water  find  their  way  into  leaky 


!n.  Lagging 


FIG.  99. — Arrangement  of  Forms  for  Arch  Culverts. 

and  defective  sewers,  entailing  a  great  burden  and  expense  on  the 
purification  plant  for  which  they  were  never  designed.  Further- 
more, the  leakage  of  sewage  through  the  lining  of  sewers  has  a 
contaminating  influence  on  the  ground,  is  very  unsanitary  and  may 
indirectly  give  rise  to  epidemics  of  disease.  Another  important 
reason  for  imperviousness  of  sewers  is  the  protection  of  the  concrete 
from  possible  destructive  action  of  sewer  gases  which  has  been 
discussed  in  Chapter  IV.  The  importance  of  waterproofing  treat- 
ment in  extensive  sewer  projects  is  beginning  to  be  recognized  and 
in  one  of  the  largest  projects,  the  Bronx  Valley  Sewer,  in  New 
York  State,  the  entire  length  has  been  protected  by  an  exterior  shield 

[292] 


Concrete  in  Sewerage  and  Drainage  Works 

of  2 -ply  coal  tar  felt  and  pitch,  following  the  method  described  in 
the  chapter  on  waterproofing.  A  dense  concrete,  properly  rein- 
forced, and  to  which  has  been  added  a  small  percentage  of  a  good 
waterproofing  compound,  or  the  interior  surface  of  which  has  been 
treated  to  two  coats  of  a  durable  and  impregnating  waterproof 
paint,  will  answer  the  purpose  very  well. 

Water-carrying  conduits  likewise  must  be  impervious,  as  other- 
wise there  will  be  not  only  a  large,  loss  of  water,  but  ground  water, 
often  polluted,  may  filter  in  and  cause  trouble.  When  expense  is  a 
secondary  consideration,  a  coat  of  waterproof  cement  may  be 
applied  to  the  interior  surface  in  accordance  with  the  specifications 
for. the  Integral  Method  as  given  in  Chapter  XXX.  Impervious 
concrete  may  be  obtained  by  scientific  proportioning  of  materials, 
as  described  in  Chapter  VI,  but  a  good  waterproofing  treatment  is 
usually  advisable. 

TABLE  XXVI. — AMOUNT  OF  MATERIALS  FOR  ARCH  CULVERTS,  f 


MATERIALS  FOR  CULVERT  FOR  IO-FOOT  ROADWAY 

EXTRA  MATERIAL  FOR  EACH  ADDITIONAL 

FOOT  WIDTH  OF  ROAD. 

Screened* 

Screened 

Span  of 
Culvert. 
Feet. 

Cement. 
Bags  Barrels. 

Sand.* 
Double 
Load. 

Gravel  or 
Stone. 
Double 

Cement. 
Bags.  Bbls. 

Sand. 
Double 
Load.* 

Gravel  or 
Stone.* 
Double 

Load. 

Load. 

5 

50  or  12$ 

3 

6 

2  or  £ 

i 

i 

8 

80  or  20 

4l 

9* 

3  or  f 

3A6 

i 

10 

115  or  28f 

7 

14 

4  or  i 

i 

* 

*  A  double  load  of  sand  or  gravel  is  taken  as  40  cubic  feet  or  about  ij  cubic 
yards. 

f  From  "Concrete  Construction  About  the  Home  and  on  the  Farm,"  published  by 
Atlas  Portland  Cement  Co. 


293] 


CHAPTER  XXVI 

CONCRETE    TANKS,    DAMS,    AND  RESERVOIRS 

Uses  of    Concrete   Tanks. — How   to   Build    Tanks. — Reinforcement   for   Tanks. — 
Concrete  Dams. — Small  Reinforced  Concrete  Dams. — Concrete  Reservoirs. 

THE  construction  of  waterworks  has  received  a  new  impetus 
with  the  development  of  concrete,  plain  and  reinforced.  Its 
durability,  adaptability  to  any  condition,  and  economy  have  made 
possible  the  erection  of  any  number  of  works  which  would  have 
been  impossible  if  more  expensive  and  less  permanent  material 
had  to  be  employed.  Concrete  has  thus  contributed  not  a  little  to 
improved  sanitary  conditions  in  water  supplies. 

In  the  collecting  and  storage  systems,  as  well  as  with  distributing 
systems  of  all  modern  waterworks,  concrete  plays  an  important  part 
and  will  continue  to  do  so  more  and  more  as  its  many  advantages 
over  other  constructive  materials  become  better  known. 

In  the  smallest  of  wells,  springs,  and  watering-troughs,  as  well 
as  in  the  largest  tanks,  reservoirs,  dams,  and  conduits,  concrete 
can  be  advantageously  employed  and  a  volume  alone  could  be 
written  on  this  branch  of  the  subject.  The  smaller  structures  used 
about  the  farm  are  discussed  in  that  chapter,  and  the  question  of 
pipes  and  conduits  has  also  been  discussed  in  other  parts  of  the 
book.  We  must  therefore  confine  ourselves  here  to  the  discussion 
of  such  typical  structures  as  tanks  and  water  towers,  reservoirs,  and 
dams. 

c 

CONCRETE  TANKS* 

Various  Uses. — Concrete  tanks  have  been  built  as  receptacles 
for  such  a  variety  of  substances  that  it  is  impossible  to  name  them 
all.  We  naturally  think  first  of  a  tank  as  a  receptacle  for  water, 

*  For  complete  directions  see  "Concrete  Tanks,"  published  by  American  Associa- 
tion of  Portland  Cement  Manufacturers,  Land  Title  Building,  Phila.,  Pa.,  from  which 
this  description  is  partly  condensed. 

[294] 


Concrete  Tanks,  Dams,  and  Reservoirs 

but  this  is  only  one  liquid  for  which  a  concrete  tank  is  suitable. 
Manufacturers  of  oil,  wine,  milk,  molasses,  pulp,  glue,  and  a  variety 
of  other  materials  are  now  using  concrete  in  the  construction  of 
their  tanks  (or  vats) ,  both  for  the  finished  product  and  in  the  course 
of  manufacture.  Vegetable  oils  are  said  to  have  a  deteriorating 
effect  upon  concrete,  but  through  the  use  of  the  very  excellent 
waterproofing  compounds  now  available,  concrete  can  be  used  in 
the  construction  of  tanks  for  these  oils.  Very  naturally,  the  use 
we  will  discuss  most  fully  is  that  of  water,  as  probably  nine-tenths 
of  the  tanks  built  are  for  the  holding  of  water.  For  other  substances, 
where  the  use  is  a  new  one,  careful  experiments  should  be  made  to 
determine  the  chemical  effect  upon  the  concrete  of  the  substance  to 
be  held.  Concrete  tanks  are  also  extensively  built  to  hold  dry  ma- 
terials, such  as  sand,  stone,  coal,  and  grain. 

Choosing  the  Location,  Size,  and  Shape. — Tanks  may  be  gener- 
ally divided  into  two  classes:  viz.,  those  above  the  ground  surface, 
and  those  below,  and  in  choosing  the  proper  design  the  tank  location 
must  be  first  selected. 

The  next  step  is  to  decide  the  shape  of  the  tank.  Tanks  are 
built  in  many  shapes,  but  the  convenience  of  use  usually  decides  the 
shape  selected. 

How  to  Build  the  Tank — Rectangular  Tanks.— Laying  Out  the 
Ground. — After  the  size  has  been  decided  upon,  select  a  site  near 
the  water-supply  if  possible,  and  mark  off  the  ground.  In  selecting 
the  size,  remember  that  71/2  gallons  make  one  cubic  foot,  and 
that  a  barrel  holds  from  49  to  54  gallons. 

Put  four  nails  in  the  ground  in  the  shape  of  a  rectangle,  to  mark 
the  outside  line  of  the  tank  walls,  and  stretch  strings  from  nail  to 
nail. 

Excavate  inside  the  space  thus  marked  to  a  depth  of  6  or  8  inches. 
If  the  soil  is  good  stiff  material,  the  bottom  of  the  tank  may  be  placed 
directly  on  this  ground. 

If  the  ground  is  soft,  dig  a  trench  just  inside  the  strings  one  foot 
deep  and  one  foot  wide  to  secure  additional  foundations. 

The  ground  under  the  proposed  tank  should  be  thoroughly 
tamped  (beaten  down),  with  as  heavy  a  tamper  as  one  or  two  men 
can  handle.  A  block  of  wood,  square  or  round,  12  or  14  inches 
across,  with  handles  for  lifting,  makes  an  excellent  tamper. 

[295] 


Handbook  for  Cement  and  Concrete  Users 


Amount  of  Reinforcement  in  Bottom  of  Tank. — The  thickness  of 
bottom  will  be  made  in  all  cases  6  inches;  for  tanks  of  this  depth 
reinforcement  must  be  placed  2  inches  from  the  bottom  of  the  slab, 
and  this  reinforcement  must  run  each  way. 

Placing  Reinforcing. — By  referring  to  the  accompanying  tables, 
we  find  it  necessary  for  a  tank  6  feet  deep  to  use  in  the  bottom  one 
J-inch  round  steel  rod  every  14  inches.  If  the  tank  is  to  be  five 
feet  square,  these  should  be  cut  in  lengths  of  5  feet  each.  Lay 
them  on  the  ground  spaced  properly,  the  rods  in  one  direction 
resting  on  the  rods  in  the  other.  Then  cut  the  rods  for  the  vertical 
reinforcement  of  the  wall.  Also  we  find  that  for  a  tank  6  feet  deep 
we  require  J-inch  round  rods  spaced  5  inches  apart.  Fifty-two  of 

TABLE  XXVII.— FOR  SPACING  OF  RODS  IN  BOTTOM  OF  TANK. 


Depth  of  Tank. 

Spacing  of  f-inch 
Round  Rods. 

Spacing  of  ^-inch 
Round  Rods. 

Spacing  of  f-inch 
Round  Rods. 

3  feet 

10    inches 

4 

8       " 

1  6  inches 

5 

7l     " 

*5     " 

6 

7      " 

14     " 

7 

61     " 

,        13     " 

8 

6       " 

12       " 

24  inches 

9 

5      " 

10       " 

20       " 

10 

4 

8     " 

16     " 

these  will  be  required.  These  rods  should  be  cut  7  feet  long. 
Make  a  hook  at  each  end  of  these  bars.  This  can  be  done  by 
placing  the  end  of  the  bar  between  two  heavy  spikes  nailed  in  a 
block  of  wood  and  bending  by  moving  the  other  end  of  the  bar. 
The  length  of  these  bars  after  they  have  been  bent  should  be  about 
6  feet  4  inches.  Rods  should  also  be  bent  for  the  horizontal  re- 
inforcing. From  Table  XXVIII,  we  see  that  for  this  sized  tank 
J-inch  round  bars  spaced  10  inches  apart  are  required.  Seven 
of  these  will  be  needed  on  a  side. 

The  i /2-inch  rods  with  hooks  at  each  end  are  placed  in  position 
by  hooking  the  lower  end  of  all  the  bars  on  one  side  under  the  rods 
in  the  bottom  reinforcing,  coming  about  2  inches  outside  the  line 
of  the  form  which  has  been  erected.  After  having  placed  these 

[296] 


Concrete  Tanks,  Dams,  and  Reservoirs 


vertical  i/ 2-inch  round  rods'in  the  correct  positions,  the  next  step 
is  to  place  the  horizontal  reinforcement  for  the  walls.  This  we 
have  previously  seen  consists  of  i/ 2-inch  round  bars  spaced  10 
inches  apart.  Where  the  bars  lap,  they  should  be  firmly  wired 
together. 

TABLE  XXVIII.— SHOWING  SIZE  AND  SPACING  OF  RODS  IN  WALL. 


SPACING  OF 

SPACING  OF 

SPACING  OF 

SPACING  OF 

Depth 

Thick- 

I-INCH ROUND 
RODS. 

J-INCH  ROUND 
RODS. 

I-INCH  ROUND 
RODS. 

I-INCH  ROUND 
RODS. 

of 

ness  of 

Tank. 

Wall. 

Verti- 

Hori- 

Verti- 

Hori- 

Verti- 

Hori- 

Verti- 

H6ri- 

cal. 

zontal. 

cal. 

zontal. 

cal. 

zontal. 

cal. 

zontal. 

Feet. 

Inches. 

Inches. 

Inches. 

Inches. 

Inches. 

Inches. 

Inches. 

Inches. 

Inches. 

3 

5 

5 

IO 

10 

20 

4 

5 

4 

8 

8 

16 

16 

32 

5 

Si 

3 

6 

6 

12 

12 

24 

6 

6* 

2| 

5 

5 

10 

10 

20 

18 

36 

7 

8 

3 

6 

7 

14 

15 

3° 

8 

9* 

2* 

5 

5 

10 

II 

22 

9 

10$ 

5 

10 

10 

2O 

10 

12 

4 

8 

8 

16 

TABLE  XXIX.— DIMENSIONS  FOR  CIRCULAR  TANKS. 


(') 

Depth. 

(2) 
Diameter. 

Thickness 
of 
Concrete 

(4) 

Diameter 
of 
Horizontal 

Q    (5> 

bpacmg 
Horizontal 
Rods  at 

(6) 
Spacing 
Horizontal 
Rods  at 

(7) 

Diameter 
Vertical 

(8) 

Spacing 
Vertical 

in  Wall. 

Rods. 

Bottom. 

Top. 

Rods. 

Rods. 

Feet. 

Feet. 

Inches. 

Inches. 

Inches. 

Inches. 

Inches. 

Inches. 

5 

5 

6 

i 

8 

18 

i 

36 

5 

10 

6 

i 

6 

12 

i 

3° 

10 

10 

8 

f 

6 

18 

I 

36 

IO 

*5 

8 

| 

4 

18 

i 

36 

J5 

10 

12 

1 

4 

18 

1 

3° 

15 

15 

12 

i 

6 

20 

1 

3° 

We  will  illustrate  the  method  of  using  Table  XXIX  in  building 
a  tank  15  feet  deep  and  10  feet  in  diameter.  From  the  table  we  see 
that  the  thickness  of  concrete  in  the  walls  of  the  tank  is  10  inches; 
that  the  size  of  reinforcement  to  be  used  is  3/8-inch  rods,  that  is, 
round  rods  3/8  of  an  inch  in  diameter;  for  the  first  foot  these  rods 
should  be  spaced  4  inches  apart,  and  the  vertical  rods  should  be 

[297] 


Handbook  for  Cement  and  Concrete  Users 

placed  30  inches  apart.  The  table  calls  for  the  spacing  of  the  hori- 
zontal rods  1 8  inches  apart  at  the  top  of  the  tank,  and  the  inter- 
mediate horizontal  rods  will  therefore  be  spaced  distances  varying 
from  1 8  inches  to  4  inches;  thus  in  the  second  foot  from  the  bottom 
the  horizontal  rods  will  be  5  inches  apart;  in  the  third  foot,  6  inches 
apart;  in  the  fourth  foot,  7  inches  apart;  in  the  fifth  foot,  8  inches 
apart;  in  the  sixth  foot,  9  inches  apart;  in  the  seventh  foot,  10  inches 
apart  ;  in  the  eighth  foot,  n  inches  apart;  in  the  ninth,  12  inches 
apart;  in  the  tenth,  13  inches  apart;  in  the  eleventh,  14  inches 
apart;  in  the  twelfth,  15  inches  apart;  in  the  thirteenth,  16  inches 
apart;  in  the  fourteenth,  17  inches  apart;  and  in  the  fifteenth,  18 

inches  apart. 

/ 

CONCRETE  DAMS 

Concrete  is  now  being  extensively  employed  in  the  construction 
of  dams  of  every  conceivable  shape  and  size.  They  are  al),  how- 
ever, of  three  general  types,  the  solid  or  gravity  type,  the  arched 
type  and  the  hollow  reinforced  type. 

The  fundamental  principles'  in  the  design  of  gravity  dams  are 
much  the  same  as  those  underlying  the  design  of  retaining  walls, 
the  main  difference  being  that  the  dam  must  not  only  be  strong 
enough  to  be  safe  against  a  full  head  of  water  in  the  reservoir,  but 
also  in  the  case  of  very  high  dams  it  must  be  safe  against  the  weight 
of  masonry  in  the  structure  itself.  Furthermore  the  external 
pressure  of  the  water  can  be  determined  with  scientific  exactness 
while  the  pressure  of  earth  on  walls  is  subject  to  many  uncertainties. 
The  amount  of  water  pressure  per  square  foot  against  a  dam  at 
any  depth  is  found  by  the  simple  rule 

P  =  62.5  H.  and  against  the  surface  one  foot  wide.  P  =  31.25  H* 

P  =  Pressure  in  Ibs.  at  any  depth  H  in  feet. 

Table  XXX  gives  the  pressures  at  different  depths: 

Gravity  dams  may  be  constructed  of  solid  concrete  or  of  concrete 
in  which  is  embedded  large  blocks  of  rubble.  The  latter  type  which 
is  called  "  Rubble  Concrete,"  or  "  Cyclopean  Masonry,"  is  by  far 
the  most  economical  as  the  amount  of  cement  required  is  reduced 
to  a  minimum. 

Small  Dams. — The  construction  of  small  dams  under  six  feet 

[298] 


Concrete  Tanks,  Dams,  and  Reservoirs 


high  may  be  undertaken  without  special  engineering  advice 
as  follows :  * 

"If  possible,  dig  a  temporary  trench  so  as  to  carry  the  water 
around  the  dam  while  it  is  being  built.  If  this  cannot  be  done,  run 
the  water  through  a  wooden  trough  in  the  middle  of  the  dam,  and 
after  the  wall  each  side  of  it  is  finished,  carry  the  forms  across  the 
opening,  and  make  these  tight  enough  so  that  the  water  is  quiet 
between  them;  then  place  the  concrete. 

"Dig  a  trench  across  the  stream  slightly  wider  than  the  width 
of  the  base  of  the  dam,  carrying  it  down  about  18  inches  or  2  feet 
below  the  bed  of  the  brook,  or  if  the  ground  is  soft,  deep  enough  to 

TABLE  XXX.— HYDROSTATIC  PRESSURES. 


Hydros  tatic^Head. 
Feet. 

Lifting  Pressure 
per  Square  Foot. 

Lbs. 

Average  Pressure 
per  Square  Foot 
on  Vertical  Surface. 
Lbs. 

°-S 

31.2 

15-6 

I  .0 

62.5 

31.2 

2  .O 

125  .0 

62  .5 

3-° 

187-5 

93-7 

4.0 

250.0 

125  .0 

5-° 

312-5 

156.2 

6.0 

375-o 

i87-5 

8.0 

500.0 

250.0 

10.  0 

625  .0 

3i2-5 

12  .0 

750.0 

375  -° 

*5-Q 

937-5 

468.7 

20.0 

1250.0 

625.0 

25  .0 

!562-5 

781.2 

30.0 

1875.0 

937-5 

4O.O 

2500.0 

1250.0 

60  .O 

375°  -o 

1875.0 

80.0 

5000  .0 

2500.0 

100.  0 

6250.0 

3I25-° 

reach  good,  hard  bottom.  In  case  the  earth  is  firm  enough  for  a 
foundation,  but  is  porous  either  under  the  dam  or  each  side  of  it, 
sheet  piling  consisting  of  2-inch  tongued-and-grooved  plank  can  be 
pointed  and  driven  with  a  heavy  wooden  mallet  so  as  to  prevent  the 
water  flowing  under  or  around  the  dam.  Build  the  forms  so  as  to 

*  From  "Concrete  Construction  About  the  Home  and  on  the  Farm,"  published  by 
Atlas  Portland  Cement  Co. 

[299] 


Handbook  for  Cement  and  Concrete  Users 


make  the  wall  of  the  dimensions  shown  in  the  table.  Wet  them 
thoroughly,  then  mix  and  place  the  concrete. 

"Use  proportions  one  part  Portland  cement  to  two  parts  clean, 
coarse  sand  to  four  parts  screened  gravel  or  broken  stone. 

"Take  special  care  to  make  the  concrete  water-tight  by  using 
a  wet  mix.  If  possible,  lay  the  entire  dam  in  one  day,  not  allowing 
one  layer  to  set  before  the  next  one  is  placed.  If  it  is  necessary  to 
lay  the  concrete  on  two  different  days,  scrape  off  the  top  surface  of 
the  old  concrete  in  the  morning,  thoroughly  soak  it  with  water,  and 
spread  on  a  layer  about  1/4  inch  thick  of  pure  cement  of  the  con- 
sistency of  thick  cream,  then  place  the  fresh  concrete  before  this 
cement  has  begun  to  stiffen. 

"If  the  forms  on  the  lower  side  of  the  dam  are  well  braced,  the 
forms  on  the  upstream  side  may  be  removed  in  three  or  four  days, 
and  the  pond  allowed  to  fill.  The  forms  on  the  down-stream  face 
should  be  left  in  place  well  braced  for  two  or  three  weeks.  No 
finish  need  be  given  to  the  surface." 

Reinforced-Concrete  Dams.f — Reinforced  concrete  is  particularly 
adapted  to  the  construction  of  dams.  When  so  used  there  is  a 

TABLE  XXXI. — DIMENSIONS  FOR  SMALL  DAMS  AND  QUANTITY 
OF  MATERIALS  FOR  DIFFERENT  HEIGHTS  OF  DAMS. 

Proportions:     i  Part  Portland  Cement  to  2  Parts  Sand  to  4  Parts  Gravel  or  Stone 


AMOUNT  OF  MATERIALS  PER  FOOT 

Height 
Above  Bed 
of   Stream. 

Depth 
Below  Bed 
of    Stream.* 

Thickness 
at  Base. 

Thickness 
at  Top. 

OF  LENGTH  OF  DAM. 

Cement. 

Sand. 

Gravel  or 
Stone. 

Feet. 

Feet. 

Feet. 

Feet. 

Bags. 

Cu.  Ft. 

Cu.  Ft. 

H. 

G. 

B. 

T. 

I 

l| 

I 

I 

i 

I 

ij 

2 

ij 

I 

I 

i 

ij 

3 

•  3 

4 

2 

l| 

if 

4 

8 

4 

2 

2 

*l 

2I 

5 

10 

5 

2 

2i 

l£ 

3* 

6| 

13^ 

6 

2 

3 

•i 

4* 

8J 

i7l 

*  Make  deeper  if  necessary  to  get  a  good  foundation. 
Note. — A  large  single  load  of  sand  or  gravel  is  about  20  cubic  feet. 
A  large  double  load  of  sand  or  gravel  is  about  40  cubic  feet. 

f  This  discussion  is  arranged  from  "Concrete,  Plain    and  Reinforced,"  by  Homer 
A.  Reid. 

[300] 


Concrete  Tanks,  Dams,  and  Reservoirs 

great  saving  in  material,  and  on  this  account  a  reduction  in  cost  of, 
in  some  cases,  as  much  as  20  per  cent.  Again,  the  space  under  the 
apron  may  be  utilized  for  storage  or  power-house  purposes,  as  for 
the  location  of  turbines,  electric  generators,  etc.  Another  advantage 
is  that  of  securing  a  practically  impervious  curtain  face  wall,  with- 
out any  of  the  dangerous  leaks  so  troublesome  to  locate  in  some 
masonry  structures.  If  sufficient  number  of  reinforcing  rods  are 
used  and  run  in  every  direction  there  will  be  little  or  no  danger  of 
cracking  in  the  deck  concrete. 

The  design  of  steel  dams  is  that^of  a  triangle  with  the  upstream 
face  so  flatly  inclined  that  the  water  pressure  is  made  to  give  in- 
creased stability  by  its  weight,  and  this  basic  principle  has  been  the 
leading  feature  in  the  development  of  dams  of  reinforced  concrete, 


FIG.  100. — Design  for  Small  Dam. 

which  were  first  introduced  in  the  Eastern  States  about  the  year 
1902  by  the  Ambursen  Hydraulic  Construction  Company,  of  Boston. 

About  30  dams  varying  in  height  from  10  to  So  feet,  some  over 
1,000  feet  long,  have  been  erected  during  the  last  8  years,  many  of 
them  attracting  marked  attention  by  the  engineering  profession. 

The  design  of  these  dams  illustrates  very  strikingly  the  adapta- 
bility of  reinforced  concrete  to  new  conditions.  The  principle 
followed  in  the  design  is  that  the  vertical  pressure  of  the  water  is 
utilized  to  firmly  hold  the  dam  down  on  its  foundation. 

[301] 


Handbook  for  Cement  and  Concrete  Users 

With  the  usual  type  of  gravity  dams,  the  up-stream  face  is  verti- 
cal or  nearly  so.  The  pressure  of  the  water  is  thus  exerted  horizon- 
tally, tending  to  overturn  the  dam,  which  must  therefore  be  made 
heavy  enough  to  prevent  same  from  occurring. 

In  the  reinforced-concrete  dam,  the  slope  of  the  water  face  may 
be  so  fixed  that  the  pressure  on  the  foundation  is  controlled  by 
the  designer,  and  the  safety  factor  is  made  at  least  five. 

The  usual  type  of  reinforced-concrete  dam  consists  of  an  in- 
clined slab  of  reinforced  concrete  extending  from  the  heel  to  the 
crest,  and  spanning  between  and  supported  by  transverse  buttresses 
of  concrete,  resting  upon  the  foundation.  Another  inclined  slab 
may  or  may  not  be  used  to  form  an  apron  or  spill-way.  The  deck 


Rot/way 


FIG.  101. — Curtain  Type  of  Reinforced  Concrete  Dam. 

is  usually  increased  in  thickness  from  the  crest  to  the  heel  on  account 
of  the  increase  in  pressure  as  the  water  deepens. 

The  principles  governing  the  design  of  reinforced-concrete 
dams  are  the  same  as  those  used  for  the  design  of  masonry 
dams  as  far  as  the  external  pressures  are  concerned.  However, 
as  reinforced-concrete  dams  are  usually  of  triangular  cross-section, 
they  have  a  much  wider  base  than  masonry  structures,  which 
greatly  increases  their  resistance  to  overturning.  This  resistance 
is  further  increased  by  the  weight  of  the  water  above  the  face 
or  deck,  which  usually  has  an  inclination  of  from  30°  to  45°  with 
the  horizontal. 

An  increase  in  the  height  of  the  water  flowing  over  a  masonry  or 
solid  dam  increases  the  pressure  thereon  and  causes  the  line  of  press- 

[302] 


Concrete  Tanks,  Dams,  and  Reservoirs 


ure  to  rise,  thereby  greatly  increasing  the  overturning  moment  on  the 
dam  without  in  any  way  increasing  the  resisting  moment  to  the  same. 


„    CONTRACT  NO.  3   SHEET  NO.  15 

j! SHEETS  IN..SET, 58   i! 
-  =Cp==  ---  =  =?e=  =  ==== =&--r^.-_-.iT==A-_--^_-= 


EgS3HB£Jf£:53!j 

SElffiHr!?!;!.  tE^as 


-  Concrete  masonry 

EITHER  FACE  AT 
ROCK  FOUNDATION 


Inspection 
gallery 

Flow  line 


Concrete  drainage 
blocks 


Drainage 


DOWNSTREAM  FACE 


I        t    »  . 


UPSTREAM  FACE 
ARRANGEMENT  OF  FACE  BLOCKS 

10    2         6         10        14        18       22Ft 


Concrete  gutter 
El.  460 


insp  ecrion_  gallery 


Assumed  line 
of  excavation 


MAXIMUM  SECTION 


FIG.  102. — Ashokan  Dam  of  the  New  Water  Supply  System  for  the  City  of  New  York. 
One  of  the  Largest  Dams  in  the  World. 

In  a  triangular  dam,  however,  with  a  broad  base,  as  in  the  hollow 
reinforced-concrete  dam,  when  the  head  of  water  flowing  over  the 
dam  is  increased,  the  lines  of  pressure  become  more  nearly  vertical, 

[303] 


Handbook  for  Cement  and  Concrete  Users 

the  overturning  moment  is  actually  reduced,  and  the  stability  is  in 
no  way  endangered.*  Owing  to  the  reduction  in  weight  it  may  be 
necessary  sometimes  to  fill  hollow  dams  with  sand,  earth,  or  gravel 
to  increase  its  resistance  to  sliding. 

Reinforced-concrete  dams  are  particularly  fitted  to  poor  founda- 
tion conditions  on  account  of  the  broad  base  and  consequent  low 
unit  pressures.  This  will  often  enable  a  large  saving  in  cost. 

Concrete  Reservoirs. — The  construction  of  reservoirs  of  concrete 
present  but  few  features  not  already  discussed  in  the  sections  on 
walls  and  dams.  The  principal  difficulty  encountered  is  in  obtaining 
a  watertight  bottom,  as  extensive  areas  of  shallow  concrete  are 
subject  to  cracking  on  account  of  settlement,  shrinkage,  and  ex- 
pansion. The  best  means  to  avoid  this  cracking  is  by  having  a 
double  lining.  The  under  lining  is  laid  in  a  continuous  sheet  and 
covered  with  a  sheet  of  a  good  asphalt ic  material,  and  over  this  is 
placed  concrete,  in  sections  ten  feet  square,  the  joints  between  the 
sections  being  filled  with  an  asphaltic  material. 


[304] 


CHAPTER  XXVII 

CONCRETE    SIDEWALKS,  CURBS,  AND   PAVEMENTS 

Advantages  of  Concrete  Sidewalks. — Materials,  Equipment,  and  Forms. — Construction 
of  the  Sidewalk. — Coloring  and  Protection. — Tables  of  Dimensions  and  Materials 
Required. — Concrete  Curbs  and  Gutters. — Concrete  Roads  and  Pavements. — 
Table  of  Offsets  for  Crowning  Roads. 

THE  class  of  work  in  which  the  value  and  adaptability  of  concrete 
has  been  brought  most  intimately  to  the  attention  of  laymen  and 
municipal  authorities  is  cement  sidewalk  construction.  Being  one 
of  the  oldest  forms  in  which  cement  has  been  employed,  its  use  in 
this  connection  has  grown  so  rapidly  that  no  important  community 
is  without  its  miles  of  well-paved  walks;  and  what  had  formerly  been 
a  luxury  employed  only  by  large  towns  and  cities,  has  now  become 
an  e very-day  necessity  in  all  progressive  communities.  In  fact,  it  is 
due  to  the  introduction  of  the  cement  walk,  that  many  hundreds 
of  communities  have  been  enabled  to  provide  themselves  with  walks 
at  all;  for  the  cement  walk  possesses  all  the  merits  of  the  older 
forms  of  wood,  brick,  and  stone,  and  few  of  their  defects,  and  the 
low  cost  and  maintenance  charges  place  it  within  the  reach  of  almost 
any  up-to-date  home. 

The  beauty,  convenience,  noiselessness,  durability,  and  economy 
of  well-constructed  walks  have  always  had  a  highly  beneficial  in- 
fluence on  property  values  wherever  they  have  been  constructed. 

Concrete  as  a  material  for  curbs  and  gutters  is  just  as  advan- 
tageous as  for  sidewalks,  and  its  adaptability  for  the  roadway  of 
streets  is  now  becoming  quite  generally  recognized  and  will  continue 
to  be  more  so  in  the  future.  The  question  of  its  use  as  a  paving 
material  is  taken  up  later  in  this  chapter. 

Materials  for  Sidewalks. — Sidewalks  should  be  constructed  only 
of  Portland  cement,  as  the  natural  and  slag  varieties  are  unfitted 
for  constant  exposure  to  the  elements.  A  good  sand  or  screenings 
and  a  clean,  hard,  and  durable  stone  should  be  employed  and  the 
same  well  graded.  Five  per  cent  of  clay  may  be  allowed.  The 
20  [  305  j 


Handbook  for  Cement  and  Concrete  Users 

same  principles  should  be  followed  in  selecting  these  materials  as 
have  been  outlined  in  Chapter  V. 

Tools  and  Equipment. — The  tools  and  equipment  employed  by 
the  sidewalk  builder  are  shown  in  the  accompanying  illustration 
and  their  use  is  there  indicated. 

Forms. — Forms  for  the  sides  are  made  of  sound  wood,  at  least 
two.  inches  thick  by  five  inches  wide,  while  the  cross  forms  and  pro- 
tection strips  may  be  of  metal.  The  forms  must  be  firmly  secured 
by  stakes  driven  at  frequent  intervals  (about  2  feet)  and  placed 
upon  proper  lines  and  grades.  Specially  designed  metal  forms 
are  economical  and  very  desirable  on  any  large  work. 

Construction. — The  foundation  of  the  sidewalk  is,  as  in  all 
other  structures,  the  most  important  element  upon  which  the 
lasting  qualities  of  the  structure  depend.  To  assure  a  good  founda- 
tion, the  soil  underneath  it  should  be  well  drained  by  means  of 
broken-stone  trenches,  tile  pipes,  or  other  suitable  means  depending 
upon  the  character  of  the  soil  and  local  drainage  facilities. 

The  soil  should  be  brought  to  the  required  elevation  of  the 
subgrade  either  by  excavation  or  fill  as  the  original  surface  may 
require.  If  in  excavation,  all  spongy  and  bad  spots  must  be  re- 
moved and  replaced  by  sand  or  other  good  material. 

If  in  fill,  the  material  should  be  wetted  and  tamped  in  layers  not 
more  than  6  or  8  inches  thick.  The  fill  should  extend  far  enough 
(at  least  2  feet)  on  either  side  to  allow  the  material  to  assume  its 
natural  slope  without  danger  of  running  from  under  the  walk. 

Preparing  the  Sub-Base. — The  subgrade  should  be  at  least  12 
inches  below  the  finished  surface  and  sJope  toward  the  curb  at  least 
1/2  inch  per  foot  for  drainage.  The  foundation  or  sub-base  should  be 
at  least  8  inches  thick,  made  of  hard  cinders,  slag,  gravel,  crushed 
stone,  or  broken  brick,  grading  from  1/4  to  4  inches  in  size. 

Concrete  Base. — In  placing,  the  under  bed  of  concrete  should 
be  well  tamped  until  its  upper  surface  is  at  the  required  height, 
about  3/4  inch  below  the  finished  surface  of  the  sidewalks. 

At .  all  driveway  crossings,  increase  the  thickness  of  sub-base 
2  to  3  inches,  and  of  the  top  1/2  inch. 

Do  not  remove  cross  forms  until  concrete  is  well  compacted  and 
set,  and  in  laying  adjoining  sections,  see  that  old  surface  is  clean 
and  free  from  loose  mortar. 


Concrete  Sidewalks,  Curbs,  and  Pavements 

Leave  expansion  joints  at  least  every  50  feet,  about  1/8  inch 
wide.  This  is  done  by  the  insertion  of  expansion  strips  which  are 
later  removed  and  replaced  by  paving  pitch  or  good  sand. 

No  block  should  contain  more  than  36  square  feet,  and  no 
dimension  should  be  more  than  6  feet. 

Never  leave  the  work  with  a  slab  partly  finished,  as  breaks 
will  be  bound  to  occur  at  such  points. 

Wearing  Surface. — The  wearing  surface  should  be  smooth  but 


ROTARY  JOINTER 

For  use  in  places 

too  small  for 

ordinary  style 


DATE  STAMP 
For  marking  walks, 
artificial  stone,  etc. 


BRASS  JOINER 
For  finishing  joints 
In  walks. 


FLUTED  ROLLER 


BOUND  CORNER 


SIDEWALK  EDGES 


For  finishing  walks    SMOOTHING  TROWEL 
ete>  For  finishing  corners 

in  gutters  etc. 


NAME  PLATE 
For  stamping  names 
of  makers  on  walks, 
artificial  stone,  etc. 


SQUARE  CORNER 
SMOOTHING  TROWELS 
For  finishing  inside 
or  outside  edges  of 
circles 

TAMP 

For  tamping  con- 
crete foundations,  etc. 


RADIUS  TOOL 


JOINTER  CENTRE  KNIFE 

For  finishing  joints        For  cutting  the  sur- 
In  cement  walks,  etc.   face  of  cement  walks 
into  f  1 


HAND  BRASS  JOINTER 
For  finishing  joints 
in  cement. 


ROUND  CORNER 
SMOOTHING  TROWEL 


INDENTING  ROLLER 
For  indenting  the 
surface  of  walks. 


DRIVEWAY  IMPRES- 
SION FRAME 
For  marking  cement 
driveways. 


FIG.  103. — Principal  Tools  Employed  in  Building  Cement  Walks. 


not  slippery  and  of  uniform  dull  color.  Mixture  i  part  cement  to 
i  or  i  i  /  2  parts  crushed  granite,  slag,  grit,  or  sand. 

The  top  surface  may  be  " tamped"  or  " floated."  The  tamping 
may  be  applied  to  the  top  3/4  inch,  which  may  be  a  specially  rich 
mixture.  The  thin  mortar  will  work  to  the  surface  which  may 
then  be  trowelled  smooth. 

The  tamping  method  will  produce  a  better  bond  with  the  base 

[307] 


Handbook  for  Cement  and  Concrete  Users 

and  cause  less  delay.  When  the  floating  method  is  used  the  mortar 
should  be  mixed  thin  and  worked  to  a  true  and  smooth  finish. 

Special  pains  should  be  taken  to  obtain  a  good  bond  of  top 
surface  to  base.  The  latter  should  be  clean  and  the  top  surface 
placed  as  soon  as  possible  after  the  base  is  tamped.  Should  the 
base  have  already  hardened,  it  should  be  drenched  and  cleaned 
and  prepared  by  a  thin  film  of  grout  before  the  top  layer  is  placed. 
The  methods  described  to  secure  good  bond  in  Chapter  XXX,  are 
likewise  applicable  to  sidewalk  work. 

The  wooden  trowel  gives  a  good  finish  and  is  somewhat  free 
from  the  excessive  smoothness  and  checking  caused  by  the  steel 
trowel.  While  the  surface  is  still  green  a  grooved  roller  or  brush 
may  be  run  over  it  to  remove  the  smoothness  and  give  a  better 
foothold  for  pedestrians. 

Coloring. — The  coloring  of  sidewalks  follows  in  a  general  way 
the  coloring  of  other  cement  work,  as  described  in  Chapter  XII. 
Certain  facts  have  been  brought  out  by  experience,  however,  which 
it  is  well  to  state  here. 

The  color  of  a  walk  will  be  affected  by : 

1.  The  consistency  of  the  mortar  and  character  of  cement  and 
aggregates. 

2.  The  steel  floating  trowel  gives  a  darker  color  than  the  wooden 
one. 

3.  The  finishing  tool. 

4.  Weather  conditions. 

5.  The  protection  of  the  surface. 

6.  The  interval  of  time  between  placing  and  finishing.     Trowel- 
ling on  partly  hardened  surface  produces  blotches. 

7.  Sunshine  will  give  lighter  color  than  shade. 

It  is  therefore  important  that  the  work  be  done  under  as  uniform 
conditions  as  possible  to  obtain  uniform  color  effect. 

Protecting  the  Walk. — The  walk  should  be  protected  against: 

1.  Rain  and  sun,  which  will  cause  pitting  of  surface.     This 
may  be  effected  by  a  layer  of  sand,  tar  paper,  canvas,  or  boards 
secured  from  displacement. 

2.  Frost.— The  method  of   laying  concrete  in  freezing  weather 
and  its  protection  described  in  Chapter  VII,  applies  as  well  to  side- 
walk construction. 

•'  [308] 


Concrete  Sidewalks,  Curbs,  and  Pavements 

3.  Against  displacement  by  growing  roots  of  trees.     This  should 
be  done  by  allowing  a  clearance  of  at  least  six  inches  all  around. 

4.  Against  walking  on  it  or  other  interference  until  thoroughly 
set. 


TABLE   XXXII. — DIMENSIONS    OF   CONCRETE   SIDEWALKS   FOR 
RESIDENCE   DISTRICTS. 


Width. 

Thickness. 

Length  of  Block. 

Area  of  Block. 

4  Feet 

3lto4" 

5  Feet 

20  sq.  ft. 

4i  " 

3*  to  4" 

6     " 

27  «     « 

5     " 

4" 

5     " 

25  "     " 

6    " 

& 

5     " 

30  "     " 

6    " 

5" 

6    " 

36  «     " 

TABLE  XXXIII.— -MATERIALS  FOR  CONCRETE  SIDEWALKS.* 


BAGS  OF  CEMENT  TO  100  SQUARE  FEET  OP 
SURFACE  AREA  OF  CONCRETE  BASE  OR 
OF  WALL. 


BAGS, OF  CEMENT  TO  100  SQUARE  FEET  OF 
MORTAR  SURFACE. 


Thickness. 
Inches. 

Proportions. 

Thickness. 
Inches. 

Proportions. 

i  :  1^:3 

1:2:4 

1:3:6 

i:  i 

i:ii 

i  :  2 

3 

8* 

61 

4! 

| 

3l 

2f 

2l 

4 

"I 

8f 

6 

1 

5 

4 

3l 

5 

Hi 

ii 

7l 

I 

7 

5* 

4l 

6 

i6| 

13* 

9l 

*4 

8i 

61 

5t 

8 

22f 

18 

12 

Jl 

10 

8 

61 

10 

28f 

221 

I5l 

If 

12 

9* 

7i 

12 

34J 

26^ 

18* 

2 

14 

ii 

9 

No.  of  Square  Feet  of  Concrete  Laid  with 

No.  of  Square  Feet  of  Mortar  Surface  Laid 

4  Bags  (i  bbl.)  of  Cement. 

with  4  Bags  (i  bbl.)  of  Cement. 

3 

47 

60 

83 

| 

114 

146 

178 

4 

36 

46 

66 

1 

80 

100 

1x8 

5 

27 

36 

52 

i 

57 

73 

89 

6 

24 

3° 

41 

Ji 

48 

60 

70 

8 

17 

22 

33 

Jl 

40 

50 

59 

10 

14 

18 

26 

if 

33 

43 

52 

12 

12 

15 

21 

2 

29 

36 

44 

*  From  "  Concrete  in  Highway  Construction,"  published  by  the  Atlas  Portland 
Cement  Co.  See  also  bulletins  of  Universal  Portland  Cement  Co.  and  Vulcanite 
Cement  Co.  on  Cement  Sidewalk  Construction. 

[309] 


Handbook  for  Cement  and  Concrete  Users 

Cost. — A  gang  of  six  men  can  lay  about  700  sq.  ft.  of  6  ft.  walk 
per  day,  having  a  4"  base  and  a  3/4"  top  coat,  at  a  cost  of  from 
10  to  14  cents  per  sq.  foot,  depending  upon  the  local  price  of  labor 
and  material. 


CONCRETE  CURBS  AND  GUTTERS 

Curbs  are  usually  6  to  8  inches  wide  and  12  to  14  inches  deep, 
6  to  7  inches  of  which  extends  above  the  surface  of  the  roadway. 
The  exposed  surface  of  the  curb  is  slightly  inclined  and  corners 
rounded  off  with  a  i-inch  radius.  As  in  the  walk,  the  curb  should 
be  underlaid  with  an  8-  or  zo-inch  layer  of  cinders.  The  gutter 


Curb  form 

Fig.  104. — Concrete  Curb  and  Gutter. 

should  be  i  i  /  2  to  3  feet  wide,  slope  toward  the  curb  and  have  7  or 
8  inches  of  concrete  overlying  a  cinder  base. 

Several  patented  devices  have  been  introduced  for  reinforcing 
curbs  against  injury  by  wheels  of  vehicles,  and  these  have  proved 
very  efficient.  The  construction  of  curbs  and  gutters  should  follow 
the  same  principles  as  to  excavation,  fill,  concreting,  etc.,  as  outlined 
for  walks.  The  following  detailed  directions  should  be  given 
careful  attention: 

Rules  for  Construction  of  Cement  Curb  and  Gutter. — i.  The 
drainage  of  foundations  should  be  of  the  same  materials  as  described 
for  sidewalk  paving,  and  similarly  placed,  using  the  methods  and 
instructions  as  previously  described. 


Concrete  Sidewalks,  Curbs,  and  Pavements 


2.  Place  in  position  forms  to  receive  the  concrete.     These  forms 
are  held  in  place  by  stakes  set  by  an  engineer  at  points  necessary 
to  accurately  designate  the  line  and  grade  of  the  proposed  curb  and 
gutter. 

3.  For  forms  use    i  1/2  to  2-inch  rough  planks.     Dimensions 
to  be  according  to  the  height  of  the  curb  and  thickness  of  the  gutter, 
or  special  metal  forms  may  be  employed. 

4.  Place  forms  in  position  and  deposit  the  concrete  base. 

5.  Cut   curb   and   gutter  entirely  through  every   six  feet.     A 
convenient  and  sure  method  is  to  use  a  piece  of  quarter-inch  sheet 
iron  the  same  form  as  the  concrete  base  of  curb  and  gutter.     Fill 
in  the  cuts  thus  formed  with  dry  sand. 


f*f®sJty+ 1       ^[w^m^a^f  wye  r  2'*y6' 


Gvrrap&OHMG  fonifz 
Fig.  105. — Combined  Concrete  Curb  and  Gutter. 


6.  After  each  batch  of  concrete  is  laid,  it  should  immediately 
be  covered  with  a  top  coat  or  wearing  surface. 

7.  Slope  the  gutter  to  meet  the  requirements  of  drainage  by 
increasing  the  thickness  of  the  top  coat  on  the  side  nearest  the 
street.     Work  to  an  even  surface  with  a  straight  edge  laid  parallel 
with  the  curb. 

8.  The  upper  face  corner  of  curb  and  angle  between  curb  and 
gutter  should  be  rounded  with  a  radius  of  i  to  i  1/2  inches. 

9.  After  getting  a  good  surface,  float  with  plasterer's  float  until 

[311] 


Handbook  for  Cement  and  Concrete  Users 

a  smooth,  even  surface  is  obtained.     This  surface  should  be  wet  or 
very  moist. 

ic.  Dust  this  surface  while  it  is  still  wet  with  granite  dust  and 
Portland  cement  mixed  half  and  half,  dusting  to  take  place  before 
the  surface  water  has  been  absorbed.  Immediately  smooth  down 
with  a  trowel,  and  do  not  let  too  great  an  interval  elapse  between 
floating  and  trowelling.  Use  a  curved  trowel  for  top  corners  of 
curb  and  angles  between  curb  and  gutter. 

11.  After  trowelling,  finish  with  a  soft  brush;  an  ordinary  hearth 
brush  or  whitewash  brush  will  do.     If  the  top  is  too  dry  sprinkle 
with  water.     The  brush  will  take  out  the  trowel  marks  and  give  an 
even  texture  and  color  to  the  finished  work. 

Cut  top  coat  directly  over  the  cuts  made  in  the  concrete  base, 
levelling  the  edges  of  the  cuts  with  a  jointer. 

12.  Protect  the  work  as  previouslv  described  under  Sidewalks. 

CONCRETE  ROADS  AND  PAVEMENTS 

The  first  true  concrete  pavement  was  laid  in  Bellefontaine,  Ohio, 
about  1893.  The  base  was  4-inch  concrete,  i  to  4  and  2-inch 
wearing  surface  i  to  i.  The  pavement  was  laid  in  5 -inch  strips 
longitudinally  starting  at  each  curb  and  cut  into  5-foot  squares. 

During  the  last  10  years,  a  great  number  of  concrete  pavements 
have  been  laid,  most  of  which  have  been  either  the  " Hassan" 
pavement  or  the  Blome  Grantwood  Block,  both  of  which  are 
patented. 

Mr.  J.  H.  Chubb  in  an  interesting  paper  read  before  the  National 
Association  of  Cement  Users,  refers  to  the  systems  of  concrete  pave- 
ments in  this  country,  and  the  following  is  quoted  from  his  paper: 

"  A  study  of  the  pavements,  and  of  the  conditions  under  which 
they  were  laid,  makes  it  quite  evident  that  a  first-class  pavement 
may  be  constructed  of  concrete  at  a  reasonable  cost.  Such  a  pave- 
ment must,  however,  be  properly  laid  with  suitable  materials,  to 
insure  satisfactory  construction. 

"A  concrete  pavement  is  easily  and  economically  cleaned,  and 
from  a  sanitary  and  aesthetic  point  of  view  is  an  ideal  pavement. 
Where  properly  laid,  such  a  pavement  offers  a  good  foothold  for 
horses,  is  very  little,  if  at  all,  more  slippery  than  brick  or  stone 


Concrete  Sidewalks,  Curbs,  and  Pavements 

block,  and  certainly  less  so  than  asphalt  or  wood  block.  ,  Its  resist- 
ance to  traction  is  probably  less  than  for  any  other  pavement,  and 
while  it  is  not  as  noiseless  as  asphalt  or  wood  block,  is  superior  to 
brick  and  stone  blocks  in  this  respect. 

"  Such  pavements  are  probably  not  adapted  to  the  heaviest  traffic 
of  our  largest  cities,  but  may  be  considered  as  suitable  in  all  places 
where  brick,  wood  block,  or  asphalt  would  be  proper;  and  adapted 
to  all  conditions  of  traffic  except  those  demanding  stone  block. 
Concrete  is  the  ideal  material  for  the  paving  of  residence  streets,  of 
alleys,  courts,  and  squares,  and  in  general  makes  an  excellent  inter- 
mediate pavement,  as  to  cost  and  durability,  between  the  stone- 
block  pavement  of  heavy  travelled  streets  and  the  macadam  of  our 
country  roads." 

Concrete  pavements  have  been  laid  by  contract  at  a  cost  of 
from  99  cents  to  $2.92  per  square  yard.  The  former  figure  is  un- 
doubtedly too  low  for  first-class  construction  even  under  the  most 
favorable  conditions,  and  $2.92,  the  cost  per  square  yard  of  the 
New  Orleans  pavement,  is  high,  owing  to  local  conditions.  Con- 
sidering the  cost  of  material  and  labor  and  the  method  of  construc- 
tion, the  estimated  cost  of  $1.95  per  square  yard  for  the  pavement 
proper  as  laid  in  Bozeman,  Montana,  is  probably  more  representa- 
tive of  the  cost  of  this  type  of  pavement ;  if  anything,  it  is  a  little  high. 

The  expensive  part  of  a  brick  block  or  asphalt  pavement  is  the 
wearing  surface.  In  the  construction  of  a  concrete  pavement  a 
comparatively  cheap  but  satisfactory  material,  and  one  that  costs 
much  less  to  lay,  is  substituted  for  these  expensive  wearing  surfaces, 
which  explains  why  this  pavement  can  be  constructed  at  a  much 
less  cost  than  for  those  now  in  general  use.  The  saving  in  cost  is 
in  the  wearing  surface,  for  practically  the  same  concrete  base 
answers  for  each  type  of  pavement. 

GENERAL   HINTS   FOR   BUILDING   CONCRETE 
PAVEMENTS 

Grading. — The  entire  width  of  the  roadway  should  be  graded  to 
a  depth  sufficient  to  lay  the  required  thickness  of  pavement. 

The  subgrade  when  properly  compacted  should  be  parallel  to 
the  finished  surface  of  the  street  and  constructed  in  the  same  general 


Handbook  for  Cement  and  Concrete  Users 

way  as  described  for  sidewalks;  that  is,  bad  spots  should  be  removed 
and  replaced  and  fills  made  in  6-inch  layers.  Heavy  rollers  and 
tampers  should  be  employed  for  compacting  the  material.  Drainage 
should  be  provided  for  in  all  cases  where  natural  drainage  does  not 
exist. 

Sub-Base. — In  clayey  and  other  water-holding  soils,  a  6-  to  10- 
inch  sub-base  of  cinders,  gravel,  or  stone  should  be  laid,  the  material 
ranging  in  size  from  1/2  inch  to  4  inches.  This  sub-base  is  wetted 
and  rolled  to  a  uniform  surface,  parallel  to  the  final  roadway. 

Pavement  Proper. — The  pavement  should  be  made  of  a  4-  to 
6-inch  base  and  a  1/2  to  2-inch  wearing  surface  depending  upon  the 
extent  of  the  traffic. 

A  wet  mixture  should  be  used  for  the  concrete  base,  but  not 
too  wet  to  creep  under  light  tamping.  This  concrete  should  be 
deposited  across  the  entire  roadway  and  well  tamped  with  8-inch 
hand  tampers,  weighing  at  least  18  pounds  each. 

Expansion  joints  should  be  provided  at  the  curbline  1/4  inch 
wide,  and  every  50  feet  across  the  street  1/2  inch  wide,  formed  by 
means  of  wooden  or  metal  strips  set  in  place.  These  are  removed 
and  replaced  by  paving  pitch. 

Wearing  Surface. — The  wearing  surface  should  be  placed 
within  an  hour  of  the  base  before  the  lacrer  begins  to  harden  much, 
and  the  laying  follow  right  along  after  the  completion  of  the  base. 
A  mixture  sufficiently  wet  to  allow  floating  without  tamping  should 
be  employed.  It  should  be  finished  with  a  wooden  float  and  brushed 
with  stiff  brooms  before  completely  hardened  and  may  be  cut  into 
any  desired  grooves  or  blocks  to  provide  good  foothold  for  horses. 

Protection. — The  pavement  should  be  protected  from  the  weather 
until  thoroughly  set,  be  kept  well  sprinkled  for  3  days  at  least,  and 
not  put  into  service  in  less  than  a  week  and  longer  if  weather  con- 
ditions have  not  been  favorable  to  proper  hardening. 

Patented  Pavements.— -The  essential  features  of  the  "Blome 
Granitoid  "  Pavement  may  be  stated  as  follows: 

1.  The  subgrade  is  prepared  7"  below  the  finished  surface. 

2.  A  5  1/2  inch  base  of  1:3:5  concrete  is  then  laid  in  sections 
extending  the  full  width  of  street. 

3.  A  i  1/2  inch  cement  mortar  wearing  surface  made  of  i  cement, 
3  parts  clean,  crushed  stone  is  laid  on  the  green  concrete  base. 

[3H] 


Concrete  Sidewalks,  Curbs,  and  Pavements 

6.  The  wearing  surface  is  grooved  into  4X9  inch  blocks,  the 
length  of  the  blocks  being  perpendicular  to  the  curb.     The  grooves 
have  rounded  edges  and  are  about  1/4  inch  deep  and  1/2  inch  wide. 

7.  Before    final  hardening,  the  wearing    surface  receives  treat- 
ment with  stiff  brushes  to  eliminate  what  may  otherwise  be  ob- 
jectionable smoothness. 

8.  To  eliminate   danger   from  temperature  changes,  expansion 
joints  are  placed  50  feet  apart  and  filled  with  paving  pitch. 


W/'cffh  of  ^/reef  l/ar/ab/e 


foundation  //?  ca^e  of  c/a 


FIG.  106. — The  Blome  Granitoid  Concrete  Pavement. 

The  Hassan  pavement  is  constructed  as  follows: 

1.  The  street  is  excavated  to  the  required  depth  of  about  6 
inches  below  grade  line. 

2.  A  layer  of  11/2  to  2  1/2  inch  crushed  stone  is  then  placed 
upon  the  subgrade  properly  prepared. 

3.  This  is  rolled  until  top  is  within  2  inches  of  finished  surface. 


TABLE  XXXIV. — OFFSETS  FOR  CROWNING  STREETS  OF 
VARIOUS  WIDTHS. 

From  "  Concrete  in  Highway  Construction,"  by  Atlas  Portland  Cement  Co. 


Width  of 

Distance 

Distance 

Roadway 
Between 

Crown. 

from 
Centre  of 

Vertical 
Offset. 

from 
Centre  of 

Vertical 
Offset. 

Curbs. 

Roadway. 

Roadway. 

Feet. 

Inches. 

Feet. 

Inches. 

Feet. 

Inches. 

24 

3 

4 

i 

8 

** 

30 

4 

5 

4/9 

10 

i  7/9 

36 

5 

6 

5/9 

12 

2  2/9 

48 

6 

8 

| 

16 

»! 

60 

8 

10 

8/9 

20 

3  5/9 

[315] 


Handbook  for  Cement  and  Concrete  Users 

4.  A  grout  mixture  of  i  part  cement  to  3  parts  fine  sand  is  then 
poured  in  the  stones  and  rolling  and  grouting  continued  until  an 
even  surface  is  obtained  and  all  voids  filled. 

5.  A  2-inch  wearing  surface  of  trap  rock  is  then  laid,  rolled,  and 
grouted  with  a  i  to  2  grout. 

6.  A  finishing  coat  of  i  cement,  i  sand  and  i  pea  size  crushed 
trap  rock  is  poured  on  and  brushed  over  the  surface. 

7.  The  pavement  then  receives  its  final  rolling,  and  is  allowed 
to  harden  for  a  week  before  being  open  to  traffic. 

8.  Expansion  joints  i  inch  wide  filled  with  tar  are  provided  for 
at  the  curbs  and  about  every  100  feet  longitudinally. 


CHAPTER  XXVIII 

CONCRETE    IN    RAILROAD    CONSTRUCTION* 

Foundations  and  Retaining  Walls. — Bridges  and  Trestles. — Train  Sheds  and  Plat- 
forms.— Signal  Towers. — Power  Houses. — Shops  and  Warehouses. — Coal  and 
Sand  Pockets. — Ash  Plants.— -Round  Houses. — Turntables,  Pits,  Tank  Supports, 
and  Bumping  Posts. — Concrete  Ties  and  Roadbed. — Posts  and  Fences. — Tele- 
graph Poles. — Tunnels. — Docks. — Reservoirs. — Elevators. 

IN  railroad  construction  perhaps  more  than  in  any  other  branch 
of  engineering  has  concrete  shown  its  versatility.  Not  only  is  it 
replacing  steel  in  construction,  but  to  an  even  greater  extent  it  has 
taken  the  place  of  stone  and  brick  masonry,  not  merely  for  founda- 
tions, but  also  for  various  railroad  structures  above  ground. 

The  classes  of  railroad  structures  in  which  concrete  is  now 
extensively  employed  or  in  which  its  use  is  extending,  are  in  part  as 
follows : 

(1)  Foundations,  retaining-walls,  piers,  and  abutments. 

(2)  Bridges  and  culverts. 

(3)  Depots,  signal-towers,  shops,  and  other  buildings. 

(4)  Coal  and  sand  stations,  roundhouses,  and  turntable-pits. 

(5)  Tank  supports,  bumping  posts,  ties,  and  roadbeds. 

(6)  Posts,  fences,  telegraph  and  power  poles. 

(7)  Tunnels  and  tunnel  lining. 

(8)  Wharves  and  docks. 

(9)  Storage  reservoirs. 

(10)  Grain  elevators. 

Many  of  these  classes  of  construction  are  described  with  more 
detail  in  other  portions  of  this  work.  In  this  chapter  only  such 
mention  can  be  made  of  each  as  will  best  serve  to  illustrate  the 
special  rdle  of  concrete  in  connection  with  railroad  economics. 

Foundations. — Concrete  has  been  used  for  foundations  in  rail- 
road construction  for  many  years.  It  was  first  employed  to  encase 

*  The  matter  in  quotations  in  this  chapter  is  reproduced  by  courtesy  of  The  Atlas 
Portland  Cement  Co.,  from  "  Concrete  in  Railroad  Construction." 

[317] 


Handbook  for  Cement  and  Concrete  Users 

the  tops  of  wooden  piles  and  form  a  level  platform  on  which  to  start 
the  masonry,  thus  forming  the  foundation  courses  of  bridge  piers 
and  abutments,  buildings,  etc.  Within  recent  years  reinforcement 
has  been  introduced,  which  distributes  the  stress,  prevents  settle- 
ment, and  saves  material. 

Retaining  Walls. — Both  plain  and  reinforced  concrete  is  in 
general  use  for  retaining  walls.  As  explained  in  a  previous  chapter 
plain  concrete  walls  are  made  heavy  enough  to  withstand  the  earth 
pressures  by  virtue  of  their  weight  alone  while  reinforced  walls 
consist  of  a  thin,  vertical  slab  attached  to  a  horizontal  base,  and 
either  braced  by  counterforts  on  the  back,  or  else  designed  as  a 
cantilever  anchored  to  the  base  slab  which  also  has  a  front  pro- 
jection, the  whole  section  being  in  the  form  of  an  inverted  T. 

Piers  and  Abutments. — Concrete  is  employed  for  bridge  piers 
either  as  filling  for  ashlar  or  cut  stone  masonry,  or  for  the  entire 
pier,  in  which  case  it  may  be  either  plain  or  reinforced.  When  of 
plain  concrete,  the  sizes  and  general  proportions  are  practically  the 
same  as  for  stone  piers.  If  reinforced  concrete  is  used  a  great 
saving  in  cost  can  be  effected  either  by  reducing  the  size  of  the 
pier  or  by  building  it  hollow  with  reinforced  walls. 

Abutments  are  built  generally  of  plain  concrete  although  rein- 
forced abutments  are  also  coming  into  use,  and  consist  essentially 
of  a  buttressed  retaining  wall,  supporting  a  heavy  reinforced  slab, 
which  forms  the  bridge  seat. 

Bridges  and  Trestles. — One  of  the  most  important  applications 
of  concrete  to  railroad  construction  is  in  the  building  of  bridges  and 
trestles.  In  addition  to  its  freedom  from  rust  and  decay  the  use  of 
concrete  represents  a  large  saving  in  maintenance  charges,  since 
such  a  structure  requires  no  paint  or  repairs. 

A  concrete  bridge  is  free  from  the  excessive  vibrations  often 
experienced  in  steel  bridges  and  from  disagreeable  noise. 

Track  is  easily  maintained  on  such  a  structure,  since  the  ordinary 
track  ties  and  ballast  take  the  place  of  the  more  cumbersome  and 
expensive  track  timber  of  a  steel  structure. 

In  the  construction  of  a  concrete  bridge  there  is  no  obstruction 
of  traffic  from  swinging  booms  as  is  the  case  when  setting  stone  of 
large  dimensions  in  masonry  bridges,  nor  so  much  difficulty  in 
securing  the  necessary  skilled  labor  during  times  when  the  building 


Concrete  in  Railroad  Construction 

trades  are  active.  The  materials  used  can  generally  be  obtained 
in  the  immediate  vicinity  of  the  bridge  site,  while  the  cost  is  con- 
siderably less  than  that  of  a  stone  structure  of  the  same  capacity. 

Owing  to  the  deteriorating  influence  of  locomotive  gases  upon 
the  under  surface  of  bridge  floors  the  construction  of  overhead 
highway  crossings  is  one  of  the  greatest  problems  which  the  railroad 
engineer  is  called  upon  to  solve. 

Steel  girders  when  unprotected  have  to  be  painted  very  frequently. 
To  do  away  with  this  expense,  old  structures  are  being  encased  in 
concrete,  and  new  ones  are  being  built  either  of  reinforced  concrete 
or  of  structural  steel  encased  in  concrete.  Bridges  thus  constructed 
are  absolutely  unaffected  by  ordinary  rust,  rot,  or  fire,  and  can  be 
designed  economically  along  artistic  lines. 

Stations  and  Train  Sheds. — "Railroads  throughout  the  country 
are  adopting  the  use  of  concrete  in  the  construction  of  railway 
stations  of  every  class,  in  many  cases  for  the  entire  structure  and  in 
others  for  integral  parts,  such  as  foundations,  platforms,  smoke 
ducts,  stairways,  and  often  for  architectural  features,  such  as 
cornices,  belt  courses,  and  platform  columns.  Its  permanence,  fire- 
resisting  qualities,  and  adaptability  to  architectural  .treatment  render 
it  a  most  satisfactory  building  material  for  both  large  and  small 
stations. 

"The  train  shed  for  the  new  Lacka wanna  passenger  terminal 
at  Hoboken,  N.  J.,  is  an  entirely  new  departure  from  the  hitherto 
considered  standard  type  of  structure  for  this  purpose.  Instead 
of  comprising  a  series  of  high  arches,  which  in  the  common  type  of 
train  shed  are  continually  enveloped  in  a  haze  of  smoke  and 'gases 
from  the  locomotives,  it  consists  essentially  of  a  system  of  low- 
arched,  short  span,  longitudinal  sections,  just  high  enough  to  clear 
the  largest  locomotives  in  use  on  the  line,  with  smoke  ducts  of  rein- 
forced concrete  through  which  the  locomotive  gases  are  discharged 
directly  into  the  open  air.  In  addition  to  the  smoke  ducts,  the  plat- 
forms, pedestals  and  footings  are  of  concrete  construction. 

"  Platforms. — While  plain  concrete  has  been  used  for  many 
years  in  the  construction  of  low  platforms  at  main  stations,  the 
adoption  of  high  platforms  on  rapid  transit  and  suburban  lines 
during  the  past  few  years  has  opened  up  a  new  field  for  reinforced 
concrete. 

[319] 


Handbook  for  Cement  and  Concrete  Users 

"The  Brooklyn  Rapid  Transit  Company,  which  operates 
elevated  railroad  lines  in  Brooklyn,  has  recently  completed  a  number 
of  stations  in  the  Flatbush  section.  At  these  stations  the  platforms 
on  either  side  of  the  track  are  about  240  feet  long  and  8  feet  wide 
and  are  constructed  of  a  reinforced-concrete  slab  carried  on  girders 
of  the  same  material  which  are  in  turn  supported  by  concrete  piers 
placed  at  20-foot  intervals. 

"  Expansion  joints  are  provided  every  60  feet  by  separating  the 
construction  entirely  with  tarred  paper. 

"The  outside  edges  of  the  platform  are  equipped  with  patent 
bulb  nosing. 

"The  fences  running  the  length  of  the  platform  and  forming 
the  guard  railings  on  the  outside  and  ends  of  the  platforms  are 
constructed  of  cement  plaster  on  metal  lath. 

"In  designing  the  platforms  a  live  load  of  150  pounds  per 
square  foot  was  assumed  and  the  concrete  was  figured  at  500  pounds 
per  square  inch  extreme  fibre  stress  in  compression,  while  the  steel 
was  allowed  to  carry  16,000  pounds  per  square  inch  in  tension. 

Signal  Towers. — "Railroads  throughout  the  country  are  ex- 
periencing a  period  of  architectural  renaissance.  Structures  which 
have  in  the  past  been  built  of  temporary  construction,  apparently 
regardless  of  outward  appearance,  are  being  replaced  by  permanent 
buildings  of  artistic  design.  This  is  particularly  true  in  the  case  of 
signal  towers,  the  old  unsightly  and  necessarily  temporary  wooden 
structures  being  superseded  either  by  entire  concrete  or  combina- 
tion concrete  and  brick  towers  of  pleasing  appearance  and  per- 
manent construction. 

"The  standard  signal  towers  of  the  electric  zone  of  the  N.  Y. 
C.  &  H.  R.  R.  R.  are  combination  brick  and  concrete  structures. 
In  these  towers,  the  footings  and  foundation  walls  below  grade  are 
of  i  :  4  :  7  i  /  2  concrete,  and  the  walls  above  grade  up  to  the  first  floor 
level  are  of  i  :  3  :  6  concrete.  All  the  sills  and  lintels,  the  coping,  the 
overhanging  bay  window  and  supporting  brackets  and  the  cornice 
are  of  i  :  2  :  4  concrete.  In  this  work  an  excellent  surface  finish  was 
obtained  by  floating  the  green  concrete  with  water  and  rubbing  it 
with  a  mortar  brick  composed  of  i  part  cement  to  2  parts  sand. 
The  roof  and  floor  construction  consists  of  1:2:4  concrete  slabs, 
reinforced  with  1/2  inch  round  rods,  supported  by  steel  I-beams. 

[320] 


Concrete  in  Railroad  Construction 

Power  Houses. — "The  electrification  of  railroad  systems,  which 
bids  fair  to  be  a  thing  of  the  near  future,  will  necessitate  the  con- 
struction of  a  large  number  of  power  stations  along  their  lines. 
The  N.  Y.,  N.  H.  &  H.  R.  R.,  which  has  electrified  its  line  between 
New  York  and  Stamford,  in  the  construction  of  a  power  house  at 
Cos  Cob,  about  three  miles  from  Stamford,  has  shown  what  can  be 
done  with  concrete  in  this  kind  of  construction. 

"The  exterior  of  this  power  house  was  designed  in  the  Spanish 
Mission  style  of  architecture,  with  very  pleasing  results.  The 
foundations,  column  footings,  and  walls  up  to  the  water  table  were 
built  of  monolithic  concrete  mixed  in  the  proportions  of  i  part 
Atlas  Portland  cement,  3  parts  sand,  and  5  parts  2-inch  crushed 
granite.  All  exposed  surfaces  of  the  walls  were  given  a  bush- 
hammered  finish.  For  the  water-table,  window  arches,  coping 
and  window  sills,  monolithic  blocks  were  used.  These  blocks  were 
built  in  special  shapes  and  composed  of  concrete  having  the  same 
proportions  as  the  other  monolithic  work.  The  facing  consisted  of 
a  mixture  of  i  part  cement  to  2  parts  sand. 

"The  walls  above  the  water-table  were  built  of  hollow  blocks, 
lo-inch  by  1 2-inch  by  24-inch,  composed  of  a  mixture  of  i  part 
cement,  3  parts  sand,  and  3  parts  11/4  inch  crushed  granite,  faced 
on  the  exterior  surface  with  a  mixture  of  i  part  of  cement  to  2  parts 
of  sand,  and  where  the  inner  surface  of  the  wall  is  exposed  with  a 
mixture  of  i  part  cement  to  4  parts  sand.  All  the  window  lintels 
were  cast  in  place,  and  consist  of  1:3:5  concrete  reinforced  with 
two  3/4-inch  trussed  bars. 

Railroad  Shops  and  Warehouses. — "The  same  advantages 
which  reinforced  concrete  possesses  over  other  materials  for  the 
construction  of  power  houses  are  equally  enjoyed  by  it  as  a  material 
for  shop  and  warehouse  buildings  for  railway  purposes." 

The  C.  R.  R.  of  N.  J.  have  recently  erected  a  mammoth  seven- 
floor  warehouse  in  Newark,  N.  J.,  having  a  length  of  360  feet,  a 
width  which  varies  from  130  to  165  feet,  and  a  storage  capacity  of 
about  1,200  carloads  of  freight.  The  first  floor  is  devoted  to  team- 
ing, the  second  to  the  freight  tracks,  and  the  basement  and  four  top 
floors  to  storage. 

In  general  the  building  consists  of  a  steel  frame  and  concrete 
walls,  with  steel  columns  and  girders  carrying  floor  slabs  of  rein- 
si  [321] 


Handbook  for  Cement  and  Concrete  Users 

forced  concrete.  Owing  to  the  presence  of  quicksand,  an  excep- 
tionally wide  spread  of  footing  was  required  which  resulted  in  the 
engineers  making  the  foundation  one  continuous  plate  of  concrete 
fifteen  inches  thick,  reinforced  with  extra  heavy  expanded  metal. 

The  walls,  which  are  embellished  with  rustications,  mouldings, 
dentils  and  cornices,  are  twenty  inches  thick  to  the  second  story, 
sixteen  inches  thick  to  the  third  story,  and  twelve  inches  thick  from 
there  up  to  the  top.  The  reinforcement  for  the  walls  consists  of 
expanded  metal  and  3/4-inch  rods  laid  horizontally  about  four  feet 
apart. 

Reinforced  concrete  is  peculiarly  adapted  to  the  construction 
of  structures  which  are  to  be  used  for  the  storage  of  coal  on  account 
of  its  fire-resisting  qualities,  permanence,  and  strength. 

Coal  and  Sand  Pockets. — The  combination  coal  and  sand  station 
built  for  the  N.  &  W.  Ry.  in  1907,  consists  of  an  elevated  coal 
pocket,  having  a  capacity  of  260  tons  of  coal,  and  a  wet  sand  storage 
house  on  the  ground  with  an  elevated  dry  sand  bin.  The  coal  is 
dumped  through  a  10  X  12  foot  track  hopper  into  a  reciprocating 
feeder  which  delivers  it  into  a  steel  bucket  elevator,  discharging 
into  a  conveyor  trough  above  for  distribution  into  the  pocket.  The 
coal  is  fed  to  the  engine  tenders  through  hinged  gates  and  over 
counterweighted  coaling  chutes.  The  wet  sand  passes  into  a  dryer, 
emptying  into  a  sand  pit  underneath,  where  it  is  scooped  up  and 
carried  by  a  sand  elevator  which  dumps  it  from  above  into  the  dry 
sand  bin.  From  this  bin  it  is  fed  to  the  engines  through  two  tele- 
scopic sand  spouts. 

In  the  construction  of  the  building,  concrete  mixed  in  the  pro- 
portion of  one  part  Atlas  Portland  cement  to  2  parts  sand  to  4 
parts  broken  stone  was  used.  The  side  walls  were  designed  on  the 
basis  of  the  computed  lateral  pressure  exerted  by  bituminous  coal 
weighing  forty-seven  pounds  per  cubic  foot.  This  gave  a  maximum 
lateral  pressure  of  two  hundred  and  forty-eight  pounds  at  the  bottom 
of  the  pocket;  and  a  vertical  pressure  on  the  bottom  slab  of  nearly 
one  thousand  pounds  per  square  foot. 

Ash-handling  Plants. — Inasmuch  as  wood  burns  and  steel 
corrodes,  it  has  long  been  a  problem  as  to  how  to  build  ash-handling 
plants  capable  of  withstanding  the  destructive  effect  of  ashes 
quenched  with  water.  The  advent  of  reinforced  concrete  into  the 


Concrete  in  Railroad  Construction 

field  of  railroad  construction  has  successfully  solved  this  problem. 
At  the  present  time  most  of  the  plants  being  built  throughout  the 
country  consist  of  a  steel  framework  which  support  bins  constructed 
of  reinforced  concrete. 

Roundhouses. — The  adaptability  of  concrete  to  roundhouse 
construction  is  clearly  demonstrated  in  the  report  submitted  on  that 
subject  by  the  Committee  on  Buildings  of  the  American  Railway 
Engineering  and  Maintenance  of  Way  Association,  before  the 
annual  convention  of  that  society  held  in  Chicago,  March,  1908. 

For  the  purpose  of  discussion,  the  roundhouse  was  considered 
divided  into  Foundations  and  Pits,  Roof,  Supporting  Columns, 
and  Outer  Walls;  and  excerpts  from  the  report  are  given  below  in 
order  named. 

Foundations  and  Pits. — "  While  in  some  cases  local  conditions 
may  favor  the  use  of  stone  or  brick  for  foundations  and  pits,  it  may 
be  stated,  as  a  general  proposition,  that  good  practice  in  roundhouse 
construction  now  requires  the  use  of  concrete  for  these  parts  of  the 
structure.  When  a  solid  foundation  cannot  be  obtained  within  a 
few  feet  below  the  floor  level  of  the  building  a  considerable  saving 
may  be  effected  by  the  use  of  reinforcement." 

Roof. — "In  economy  of  first  cost,  durability  and  fire-resisting 
qualities,  there  is  no  other  fireproof  roof  construction  which  is  equal 
to  reinforced  concrete.  Steel  except  as  a  reinforcement  for  concrete, 
is  not  a  satisfactory  material  for  engine  house  roof  construction." 

Supporting  Columns. — "If  the  roof  is  of  reinforced  concrete,  it 
should  be  supported  by  columns  of  the  same  material  in  the  outer 
and  end  walls,  as  well  as  in  the  interior  of  the  building.  These 
columns  should  be  concreted  with  the  roof,  the  concrete  being  run 
into  the  forms  from  above.  The  columns  on  the  inner  circle  to 
which  the  doors  are  attached  should  be  of  some  other  material  than 
concrete,  preferably  steel  or  cast  iron." 

Outer  Walls. — "For  a  structure  roofed  with  reinforced  concrete, 
the  curtain  walls  may  be  of  brick,  plain  concrete,  reinforced  concrete, 
or  plaster.  Concrete  will,  if  properly  made,  give  good  service  and 
local  costs  of  materials  and  labor  would  ordinarily  determine  which 
of  the  first  three  styles  of  curtain  walls  named  above  should  be  built. 
The  plaster  curtain  wall  may  be  used  where  it  is  desirable  or  neces- 
sary to  reduce  the  first  cost  to  a  minimum. 

[323] 


Handbook  for  Cement  and  Concrete  Users 

"To  build  such  a  wall  Portland  cement  is  mixed  with  enough 
lime  so  that  it  can  be  worked  with  a  trowel  and  is  plastered  on 
expanded  metal.  The  latter  is  stiffened  with  rods  and  channel 
irons,  which  are  used  to  support  the  window  frames.  A  wall  of 
this  character  can  be  built  more  quickly  than  a  concrete  wall,  is 
efficient  and  should  be  durable.  If  damaged  by  a  locomotive  or 
otherwise,  it  is  easily  repaired,  and  alterations  can  be  readily  made. 
Used  with  concrete  columns,  it  should  not  crack,  and  its  first  cost 
is  but  about  half  that  of  a  brick  wall." 

Cost. — "The  cost  of  concrete  construction  in  roundhouses  de- 
pends largely  upon  the  number  of  times  the  forms  can  be  used. 
If  follows,  therefore,  that  where  the  structure  is  large  and  the 
forms  for  each  unit  or  stall  can  be  used  many  times  in  the  same 
roundhouse,  the  cost  per  stall  is  much  less  than  in  a  small  building. 
Consequently  reinforced-concrete  construction  is  more  economical 
in  large  than  in  small  roundhouses,  when  compared  with  brick  or 
frame  construction." 

Turntable  Pits,  Tank  Supports,  and  Bumping  Posts.— " In 
connection  with  roundhouse  construction  the  subject  of  turntable 
pits  is  of  special  interest.  The  facility  and  cheapness  with  which 
concrete  pits  can  be  built  is  so  generally  recognized  that  practically 
all  turntable  pits  constructed  to-day  are  built  of  concrete. 

"  Owing  to  its  strength,  rigidity,  and  resistance  to  fire  and  decay, 
reinforced  concrete  is  well  suited  for  the  construction  of  water-tank 
supports." 

Such  supports  are  octagonal  in  form  and  consist  of  reinforced- 
concrete  columns,  strongly  braced,  and  supporting  a  platform  from 
20  to  40  feet  high.  The  columns  may  be  reinforced  with  old  rails 
or  with  the  usual  bar  and  hoop  reinforcement.  The  platform 
should  be  about  9  inches  thick,  and  strongly  reinforced  to  sustain 
the  weight  of  the  tank. 

"A  bumping  post,  to  insure  safety  against  rotating  or  breaking 
down  under  constant  buffing,  should  be  constructed  so  as  to  be 
anchored  in  the  earth  direct  rather  than  attached  to  the  track  itself, 
as  is  the  case  with  practically  all  of  the  patented  posts  now  in  use 
on  railways  in  this  country.  By  the  use  of  concrete,  bumping 
posts  can  be  constructed  economically  so  as  to  meet  the  conditions 
of  stability  and  permanence." 

[324] 


Concrete  in  Railroad  Construction 

Concrete  Ties  and  Roadbeds. — One  of  the  most  serious  and 
perplexing  questions  which  confront  the  railroad  engineer  of  to-day 
is  the  tie  problem.  As  an  evidence  of  this,  during  the  year  1907, 
the  railroads  of  the  United  States  used  approximately  118,000,000 
ties,  a  very  large  percentage  of  which  were  renewals. 

This  vast  inroad  upon  the  limited  and  rapidly  decreasing  supply 
of  timber  has  caused  wooden  ties  to  become  poor  in  quality  and 
high  in  price,  with  the  result  that  railroad  engineers  are  beginning 
to  realize  the  necessity  of  procuring  a  substitute.  Many  roads 
have  been  experimenting  with  concrete  ties  of  various  designs  during 
the  past  few  years.  While  none  of  these  have  been  tested  long 


FIG.  107. — The  Kneedler.     One  of  Many  Forms  of  Concrete  Ties. 

enough  under  heavy  and  high  speed  traffic  to  warrant  the  selection 
of  any  one  as  a  proper  substitute  for  wooden  ties  under  all  con- 
ditions the  success  of  some  of  the  ties  tested-  thus  far  has  been  great 
enough  to  convince  railroad  engineers  who  have  given  the  most 
study  to  the  subject  that  a  properly  reinforced  concrete  tie  with 
proper  fastenings,  is  both  practical  and  economical,  especially  for 
tracks  where  the  speed  is  low  and  where  conditions  are  adverse  to 
the  life  of  wood  or  metal.  Without  question  concrete  ties  are  en- 
tirely suitable  and  economical  for  use  in  yards  and  sidings  and  for 
this  purpose  alone  there  is  an  enormous  field  for  their  installation 
and  use. 

Concrete  ties  possess  certain  natural  advantages  over    either 
timber  or  steel  inasmuch  as  dampness,  drawn  fires,  and  insects  have 

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Handbook  for  Cement  and  Concrete  Users 

absolutely  no  effect  upon  them.  In  addition,  they  are  practically 
independent  of  the  steel  and  timber  market,  and  can  be  made 
along  the  line  of  the  railroad,  and,  as  compared  with  the  chemically 
treated  timber  or  the  steel  tie,  at  a  reasonable  cost. 

Concrete  ties  have  been  for  about  ten  years  in  successful  use  in 
Indo-China,  where  a  very  peculiar  species  of  ant  destroys  wooden  ties 
in  a  few  months.  At  the  present  time  it  is  estimated  that  there 
are  over  1,000,000  of  these  ties  in  service.  They  are  of  an  inverted 
T-section,  the  flange  of  which  is  laid  on  the  ground,  the  stem  being 
vertical.  The  rails  are  fastened  by  bolts  which  are  embedded  in 
an  enlargement  of  the  stem  where  the  rails  pass.  In  Italy  concrete 
ties  have  been  tried  with  such  success  that  the  Italian  government 
has  recently  placed  an  order  with  various  manufacturers  in  Italy 
for  300,000  concrete  ties.' 

In  the  design  of  a  successful  tie  there  are  a  number  of  important 
functions  that  seem  to  be  more  or  less  overlooked  in  many  of  the 
ties  thus  far  built. 

Cushion  blocks,  if  used,  should  be  removable,  and  the  fastenings 
should  be  of  such  a  nature  that  they  will  not  tend  to  shake  loose. 
They  should  also  be  easily  accessible,  so  that  they  can  be  renewed 
when  injured. 

Inasmuch  as  automatic  block  signalling  is  being  extended  very 
rapidly  upon  practically  all  of  the  railroads,  it  is  important  that  the 
rails  should  be  insulated,  and  therefore  it  is  necessary  to  place 
sufficient  concrete  between  the  metal  in  contact  with  the  rails  and 
the  longitudinal  reinforcement. 

Many  long  ties  have  failed  from  the  fact  that  they  were  not 
designed  to  act  as  cantilever  beams,  thus  being  unable  to  withstand 
the  severe  shocks  coupled  with  the  sinking  of  the  tie  under  passing 
loads  on  centre  bound  track.  The  difficulty  experienced  with  tie 
blocks  has  been  in  keeping  them  in  longitudinal  position  and 
maintaining  them  so  that  the  vertical  deflection  of  one  rail  will  not 
greatly  exceed  that  of  the  other,  thereby  causing  rolling  and  pound- 
ing of  the  equipment. ' 

Finally,  ties  should  be  of  sufficient  strength  to  support  derailed 
cars  and  engines  until  they  are  off  the  ends  of  the  ties  and  actually 
into  the  ditch;  otherwise,  an  ordinary  derailment  may  become  a 
serious  wreck. 

[326] 


Concrete  in  Railroad  Construction 

Solid  Concrete  Roadbeds. — While  the  original  cost  of  a  solid 
concrete  roadbed  is  greater  than  the  ordinary  cross-tie  con- 
struction, it  is  undoubtedly  more  economical  in  the  end  for 
tunnels  and  subways;  especially  if  the  space  be  cramped,  traffic 
heavy,  and  a  track  cannot  be  temporarily  abandoned;  also 
where  the  running  rails,  guard  rails,  and  third  rails  are  attached 
to  long  ties  (as  in  the  case  of  electrified  lines),  it  is  extremely 
difficult  and  very  expensive  to  maintain  and  tamp  up  track  to 
surface  and  make  tie  renewals. 

A  solid  roadbed  can  also  be  used  to  great  advantage  and  economy 
in  rock  and  earth  cuts  where  there  is  always  a  large  maintenance 
expense  to  keep  ditches  open  and  track  in  good  surface. 

In  addition  to  the  question  of  ultimate  economy,  the  solid  con- 
crete roadbed  is  especially  commendable  for  tunnel  and  subway 


•/,•:.•&: ../'  iv  ^v:v  •••:•:/•:•  '«v  •;••••••  ••-:;;" 

•>*».•. ••''>'*.< ••'*•*••   •»•*-•.  Vi.'/^;»/ — •. .  ..-C^....^,-*^-*^'."- 


FIG.  108. — Concrete  in  Trackwork:   Hudson  Terminal  Station,  New  York. 

construction  from  a  hygienic  standpoint;  for  in  most  tunnels  and 
subways  ventilation  is  difficult  and  the  accumulation  of  grease,  dirt, 
and  debris,  which  is  readily  held  by  the  ballast  of  the  cross-tie 
track  construction,  is  a  serious  menace  to  the  health  of  the  passen- 
gers. This  danger  can  be  eliminated  in  the  solid  concrete  con- 
struction, as  the  entire  roadbed  can  be  flushed  with  water  and  kept 
in  a  neat,  clean,  and  sanitary  condition. 

Posts  and  Fences. — The  growing  scarcity  and  the  increasing 
cost  of  suitable  timber  for  posts  has  brought  concrete  into  quite 
general  use.  Concrete  posts  possess  the  advantage  over  wooden 
ones  not  only  of  unlimited  life,  greater  strength,  and  resistance  to 
action  of  fire  and  decay,  but  also  they  present  a  more  pleasing 
appearance. 

It  would  seem  that  the  concrete  post  is  particularly  adapted  to 
railroad  use.  Most  of  the  post  machines  are  cheap  and  portable 

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Handbook  for  Cement  and  Concrete  Users 

and  the  materials  employed  are  in  daily  use  on  all  roads  using 
concrete.     The  materials  are  cheap  and  easily  obtained. 

The  Lake  Shore  and  Michigan  Southern  Railway  use  concrete 
whistle  posts,  made  in  moulds  like  blocks,  which  are  31/2  inches 
thick,  12  inches  wide,  and  are  set  about  51/2  feet  above  the  ground. 
The  letters  and  signs  are  cast  right  in  the  post  and  are  painted  black. 

In  places  where  a  substantial  fence  is  required,  ultimate  economy, 
strength,  durability,  and  a  pleasing  appearance  can  be  attained 
by  the  use  of  reinforced  concrete.  Two  types  of  concrete  fences 
have  been  tried  with  success,  viz.,  solid  reinforced  concrete  and 
cement  plaster  on  metal  lath. 

The  solid  type  of  fence  generally  consists  of  a  vertical  slab  of 
reinforced  concrete  about  3  inches  thick  with  a  rounded  moulding 
like  a  hand  rail  on  the  upper  horizontal  edge. 

Telegraph  Poles. — Owing  to  the  increasing  scarcity  and  inferior 
quality  of  wood,  which  has  heretofore  been  used  exclusively  for 
telegraph  and  trolley  poles,  engineers  have  been  experimenting 
with  reinforced  concrete  for  a  number  of  years  with  the  result  that 
poles  have  been  designed  which  are  meeting  the  requirements  in 
every  way. 

Among  the  advantages  of  the  reinforced-concrete  pole,  the 
following  are  worthy  of  special  mention:  (i)  Lines  thus  equipped 
have  practically  no  trouble  from  lightning,  the  reinforcing  rods 
apparently  acting  as  conductors  of  electricity;  (2)  the  poles  require 
no  preservative  or  paint  to  protect  them  from  the  ravages  of  the 
weather,  as  is  the  case  with  wood  or  steel ;  and  (3)  the  material  is 
elastic  enough  to  withstand  all  ordinary  shocks. 

Tunnels  and  Tunnel  Lining. — One  of  the  most  common  uses  of 
both  plain  and  reinforced  concrete  is  in  the  construction  of  tunnels 
and  subways.  The  term  tunnel,  as  generally  understood  by  railroad 
engineers,  is  applied  to  construction  under  cover,  in  which  the 
tunnel  bore  is  advanced  by  drifting,  the  surface  of  the  ground  above 
the  work  not  being  disturbed.  The  term  subway  is  applied  to 
open  cut  construction.  A  tunnel  for  heavy  and  fast  railroad  traffic 
should  be  built  with  a  concrete  lining,  and  for  still  greater  economy 
the  roadbed  should  also  be  constructed  of  this  material.  The  old 
Bergen  Hill  tunnel  on  the  Lacka wanna  Railroad  is  lined  with  brick 
for  a  portion  of  its  length,  yet  fourteen  men  are  at  work  every  night 


Concrete  in  Railroad  Construction 

in  the  year  inspecting  the  lining  and  repairing  the  track.  This  ex- 
pensive and  dangerous  maintenance  work,  which  costs  annually 
about  $6,000,  is  practically  eliminated  in  the  new  tunnel  described 
below,  which  is  built  with  the  entire  lining  and  roadbed  of  concrete. 

This  tunnel  is  30  feet  wide  in  the  clear,  23  feet  5  inches  high 
from  the  base  of  the  rail  to  the  crown  of  the  roof  arch,  and  has  a 
concrete  lining  of  a  minimum  thickness  of  two  feet.  The  length  of 
the  tunnel  is  4,280  feet  and  at  two  points  located  at  about  one-third 
the  length  of  the  tunnel  from  each  portal  it  is  connected  to  the  old 
tunnel,  which  is  immediately  alongside  the  new,  by  an  open  cut 
extending  across  the  four  tracks,  100  feet  long  and  80  feet  wide. 

At  about  the  centre  of  the  sections,  into  which  these  open  cuts 
divide  the  tunnel,  shafts  10  feet  long  and  30  feet  wide  were  sunk  to 
the  new  tunnel.  These  shafts  and  open  cuts  were  used  to  good 
advantage  in  moving  the  waste  material  from  the  headings  and  they 
also  greatly  facilitated  the  work  of  placing  the  concrete  lining. 

Docks. — Inasmuch  as  practically  every  railroad  system  in  the 
country  owns  valuable  water  front  the  question  of  dock  construction 
is  a  most  important  one.  The  recent  terrible  fires  with  their  attend- 
ant devastation  along  the  water  fronts  of  Hoboken  and  of  Boston, 
have  demonstrated  only  too  clearly  the  absolute  necessity  of  positive 
fire  protection  in  structures  of  this  nature.  The  new  piers  which  the 
Delaware,  Lackawanna  and  Western  Railroad  have  designed  to 
replace  those  burned  down  in  the  Hoboken  fire  of  1904  are  to  be 
built  entirely  of  concrete  construction  from  the  cut-off  of  the 
piles. 

In  the  tropics  where  the  waters  are  infested  with  the  teredo  and 
limnoria  terebrans,  either  of  which  will  destroy  a  wooden  pile  in  a  few 
years,  and  where  the  very  atmosphere  itself  eats  away  unprotected 
wooden  and  steel  structures,  reinforced  concrete  is  especially  adapted 
to  the  construction  of  wharves  and  warehouses.  Practically  all  the 
docks  of  any  magnitude  now  being  constructed  in  South  and 
Central  America  and  the  Philippines  are  designed  as  entire  concrete 
structures. 

Storage  Reservoirs.— The  advent  of  power  construction  into  the 
field  of  railroad  engineering  incidentally  introduces  another  problem 
for  railroad  engineers  in  the  subject  of  storage  reservoirs  for  supply- 
ing these  plants  with  water. 

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Handbook  for  Cement  and  Concrete  Users 

Reinforced  concrete  has  been  used  extensively  in  the  construction 
of  reservoirs,  and  when  properly  designed  and  constructed  is  a  most 
suitable  material  on  account  of  its  durability  and  adaptability  to 
lighter  design  than  common  masonry.  For  large  or  small  tanks  it  is 
usually  cheaper  than  steel  and  requires  no  repairs. 

Reservoirs  are  built  most  economically  of  circular  form,  and  all 
the  tensile  stresses  must  be  taken  by  the  steel  hoops. 

In  building  water  tanks,  the  materials  for  the  concrete  must  be 
very  carefully  proportioned  so  as  to  give  a  watertight  wall,  and  the 
stone  should  be  of  such  size  that  a  good  surface  can  be  easily  ob- 
tained. The  proportions  used  to  resist  the  percolation  of  water 
usually  range  from  i  :  2  :  2  to  i  :  2  1/4  :  4,  the  most  common  mixture 
being  1:2:4. 

The  concrete  should  be  mixed  so  that  it  will  entirely  cover  the 
reinforcing  metal  and  flow  against  the  form.  It  is  absolutely 
essential  that  the  concreting  for  the  entire  tank  should  be  done  in  one 
operation,  or  else  that  the  surface  be  specially  prepared  and  treated 
to  make  water-tight  joints. 

Grain  Elevators. — Reinforced  concrete  is  especially  adapted  to 
the  construction  of  grain  elevators  or  other  structures  to  be  used  for 
the  storage  of  grain  on  account  of  its  being  absolutely  proof  against 
fire,  water,  or  dampness,  dust  and  vermin;  which  are  all  important 
and  essential  qualities  of  the  ideal  grain  elevator. 

Grain  elevators  may  be  grouped  into  two  classes  according  to  the 
arrangement  of  the  bins  and  elevating  machinery;  viz.,  elevators 
which  are  self-contained,  with  all  the  storage  bins  in  the  main  eleva- 
tor or  working  house;  and  elevators  consisting  of  a  working  house 
which  contains  the  elevating  machinery  and  storage  bins  connected 
with  the  working  house  by  conveyors.  Reinforced-concrete  eleva- 
tors are  commonly  built  of  the  latter  type,  with  a  working  house  that ,. 
is  generally  rectangular  in  shape  with  either  square  or  circular  bins 
connected  with  the  independent  storage  bins,  which  are  usually 
circular. 

Concrete  is  being  used  in  enormous  quantities  at  the  present  time 
by  all  of  the  leading  railroads  in  the  United  States.  Prominent 
among  these  may  be  mentioned: 

The  New  York  Central  and  Hudson  River  Railroad  in  the  con- 
struction of  its  new  passenger  terminal  in  New  York. 

[330] 


Concrete  in  Railroad  Construction 

The  Pennsylvania  Railroad  in  the  construction  of  its  new  depot 
in  New  York,  the  tunnels  under  the  North  and  East  Rivers,  and  the 
yards  at  Long  Island  City. 

The  Chicago,  Burlington  and  Quincy  Railroad  in  connection 
with  its  track  elevation  work  in  Chicago,  and  in  its  work  of  replacing 
wooden  with  reinforced  concrete  trestles  throughout  its  system. 


1 331] 


CHAPTER  XXIX 

THE  UTILITY  OF  CONCRETE  ON  THE  FARM* 

Advantages  of  Concrete  for  the  Farmer. — Concrete  Types  Found  on  the  Farm. — 
Posts. — Troughs. — Tanks. — Farm  Drainage. — Cisterns. — Cess  Pools. — Stalls. 
— Silos. — Miscellaneous. — Useful  Hints  for  the  Farmer. 

Advantages  of  Concrete  for  the  Farmer. — Concrete,  both  plain 
and  reinforced,  has  provided  the  farmer  with  an  entirely  new  build- 
ing material.  Indestructible,  economical,  and  fireproof,  it  offers, 
under  most  conditions,  features  of  advantage  over  every  other  type 
of  construction.  Concrete  has  long  been  recognized  as  the  ideal 
building  material  for  heavy  construction  and  is  now  looked  upon 
with  equal  regard  for  the  purpose  of  the  lighter  forms  of  construction 
found  necessary  on  the  progressive  and  up-to-date  farm. 

During  the  past  few  years  the  price  of  lumber  has  advanced  to 
almost  prohibitive  figures,  and  therefore  it  is  natural  that  a  sub- 
stitute material  which  is  both  cheap  and  durable,  sanitary  and 
beautiful,  should  gain  the  recognition  which  it  deserves. 

The  cost  of  concrete  work  is  variable  with  the  conditions  under 
which  the  work  is  performed.  It  is  generally  cheap  for  the  farm 
structure,  because  the  work  can  be  done  by  the  farmer  at  odd  times, 
with  comparatively  cheap  help,  as  it  is  unnecessary  to  employ 
masons  or  carpenters. 

The  lumber  for  the  forms  is  expensive,  but  it  can  be  used  again, 
generally,  for  other  purposes.  Contractors  in  concrete  construc- 
tion figure  to  save  30  per  cent  of  the  form  lumber  for  subsequent 
use. 

If  the  farmer  hires  carpenters  and  laborers  to  do  the  work,  his 
concrete  structure  will  have  a  larger  first  cost  than  wood  construc- 
tion, but  it  will  neither  decay  nor  burn  and  will  be  the  cheapest 
in  the  end. 

*  Partly  condensed  from  "  Concrete  about  the  Home  and  on  the  Farm,"  pub- 
lished by  Atlas  Portland  Cement  Co.  See  also  bulletins  on  Concrete  Tanks  and 
Concrete  Silos  published  by  American  Association  of  Portland  Cement  Manufacturers. 

[332] 


The  Utility  of  Concrete  on  the  Farm 

Concrete  Types  Found  on  the  Farm. — A  competent  engineer  or 
architect  should  always  be  employed  or  consulted  in  the  preparation 
of  plans  for  houses,  barns,  or  other  structures  of  any  magnitude; 
but  by  carefully  following  authentic  rules  and  specifications,  the 
inexperienced  farmer  can  safely  undertake  reinforced-concrete 
construction  of  simple  structures. 

Concrete  is  found  on  the  farm  in  the  following  forms:  Posts  of 
all  kinds,  troughs  and  tanks  for  various  purposes,  walls  of  all  de- 
scriptions, blocks  of  all  styles,  steps  and  stairs,  side-walls,  curbs, 
and  gutters,  drains,  floors,  stalls,  and  pens,  silos,  corn  cribs  and 
grain  elevators,  houses,  barns,  and  cellars,  and  in  many  miscellan- 
eous forms  too  numerous  to  mention. 

Fence  Posts.— Concrete  fence  posts  may  be  considered  as  typical 
of  post  construction.  They  are  generally  made  with  a  square  or 
rectangular  cross-section,  the  length  depending  upon  the  height 
desired  above  ground.  The  amount  to  be  placed  underground 
depends  upon  the  depth  of  the  frost  line  which  is  sometimes  3  or  4 
feet.  It  is  customary  to  make  them  slightly  larger  than  the  wooden 
posts  which  would  be  used  for  the  same  purposes,  the  average  cross- 
section  being  about  25  square  inches.  The  making  of  fence  posts 
has  already  been  described  in  Chapter  XV. 

Hitching  Posts,  Clothes  Posts,  Horse  Blocks. — Hitching  posts 
and  clothes  posts  may  be  made  in  a  similar  manner,  round  if  desired, 
and  reinforced  with  3/8"  iron  rods  if  more  than  7  feet  long. 

Horse  blocks  are  so  heavy  that  they  are  generally  cast  in 
place.  An  ordinary  box  form  will  serve  the  purpose.  It  is 
best  not  to  plaster  the  top  or  sides,  for  it  is  apt  to  crack  or  peel 
off.  Trowel  the  surface  when  the  concrete  is  first  laid.  Care 
should  be  used  in  the  preparation  of  a  foundation  to  prevent 
unequal  settlement. 

Concrete  Watering-Troughs. — A  concrete  watering-trough  is 
one  of  the  easiest  and  simplest  tanks  that  can  be  made  of  concrete, 
and  will  never  rot.  They  are  frequently  built  not  only  in  the  barn- 
yard or  near  the  house,  but,  where  large  numbers  of  stock  are 
pastured,  they  are  built  in  the  fields,  to  hold  water  from  a  small 
spring  which  would  not  otherwise  be  available. 

Watering-troughs  may  be  made  with  or  without  reinforcement, 
the  difference  being  that  between  a  5-  and  8-inch  wall.  Typical 

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Handbook  for  Cement  and  Concrete  Users 

dimensions  are  10  ft.  long,  2  ft.  wide,  2  ft.  deep,  5  in.  thick,  which 
may  be  varied  at  will. 

The  reinforcement  may  be  done  by  placing  a  2  1/2  inch  layer 
of  concrete  in  the  form,  and  immediately  after  placing  and  before 
the  concrete  has  set,  place  a  sheet  of  woven  fence  wire  or  some  other 
wire  fabric  over  the  concrete,  bending  it  up  so  that  it  will  come  to 
within  one  inch  of  the  top  of  the  forms  at  the  sides  and  ends.  Place 
21/2  inches  more  of  the  concrete  in  the  bottom  and  ram  lightly  to 
bring  the  mortar  to  the  surface  and  smooth  it  off  evenly.  Have 
the  inner  form  all  ready  and  as  soon  as  the  base  is  laid  and  before 
it  has  begun  to  stiffen  set  it,  taking  care  to  keep  it  at  equal  distances 


FIG.  109. — Watering-trough,  Forms,  and  Bracing. 

from  the  sides,  and  then  immediately  fill  in  the  concrete  between  the 
outer  and  inner  forms  to  the  required  height. 

Small  troughs  have  been  built  at  as  low  a  cost  as  $5.00. 

Dipping  Tanks,  Hog  Troughs,  Slop  Tanks,  Fertilizing  Tanks. — 
Dipping  tanks  for  disinfection,  hog  troughs  for  feeding,  slop  tanks 
for  heating  food  in  cold  weather,  fertilizing  tanks  for  containing 
fertilizing  fluids,  have  all  been  made  of  concrete  and  have  given 
satisfaction.  Methods  of  procedure  in  such  construction  will 
readily  suggest  themselves. 

Barn  and  cellar  floors  may  be  made  after  the  manner  of  side- 
walks, the  barn  floor  requiring  a  porous  sub-base  from  6  to  12 

[334] 


The  Utility  of  Concrete  on  the  Farm 


inches  thick  while  the  cellar  floor  can  be  laid  directly  on  the  earth 
which  should  be  evened  off  and  tamped  hard.  Waterproofing  is 
sometimes  desirable.  Feeding  floors  of  concrete  have  been  found 
advantageous  for  the  spreading  of  fodder. 

Farm  Drainage.— Farm  drainage  is  an  important  problem  and 
concrete  its  most  practical  solution.  Drains  may  be  made  in  place 
by  digging  a  trench  with  sufficient  grade  to  flush  well,  and  setting 
forms  of  the  shape  of  the  inside  of  the  drain,  so  that  the  concrete 
will  be  from  3  to  4  inches  thick.  If  a  tile  drain  is  preferred,  they 
may  be  made  from  concrete  in  the  following  manner:  Use  i  part 


P 

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FIG.  ii 

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D.  —  Forms  for  Watering-trough.     Section  through  Centre. 

of  cement  to  3  of  clean  sand.  "  One  or  two  sets  of  forms  with  four 
or  six  tile  each  may  be  made  so  that  they  can  be  filled  every  morn- 
ing, and  in  this  way  enough  tiles  can  soon  be  on  hand  to  drain  a 
large  acreage  of  land.  The  concrete  tile  should  be  made  with  a 
circular  bore,  and  may  be  either  circular,  or  square  on  the  outside." 
"Use  ordinary  stove  pipe  of  the  required  diameter  for  the  inside 
mould;  this  should  project  far  enough  above  the  top  of  the  wood 
form  so  that  a  good  grip  can  be  had  on  it  in  order  to  remove  it  from 
the  concrete.  If  desired,  holes  can  be  punched  through  the  stove- 
pipe near  the  top  and  a  rod  placed  through  these  holes  in  order  to 

[335] 


Handbook  for  Cement  and  Concrete  Users 

more  easily  withdraw  the  pipes.  To  keep  the  pipes  in  place  when 
pouring  the  concrete  for  each  tile,  drive  four  nails  in  the  floor  or 
platform  on  which  the  tile  are  to  be  cast,  leaving  them  projecting 
so  as  to  locate  the  end  of  the  pipe  and  keep  it  from  getting  out  of 
position  but  yet  not  hindering  its  removal.  The  stove  pipes  must 
be  thoroughly  cleaned  and  greased  each  time  they  are  used,  and 
must  not  be  dented  or  have  any  irregularities  on  them  to  make  them 
catch." 

"The  time  to  remove  the  stove  pipe  core  varies  with  the  wetness 
of  the  mix  and  the  temperature,  but  it  should  be  pulled  as  soon  as 


FIG.  in. — Forms  for  Square  Trough. 

the  top  of  the  concrete  begins  to  harden,  which  generally  is  from 
one-half  to  one  hour;  if  left  too  long  it  is  very  hard  to  get  them  out. 
The  outside  forms  can  usually  be  removed  after  two  or  three  hours, 
or  may  be  left  until  the  next  morning.  To  remove  the  wood  forms, 
pull  the  protruding  nails  with  a  claw  hammer,  and  carefully  turn 
the  whole  tier  on  the  side.  Next  draw  out  the  other  side  with  the 
partitions  attached.  If  any  of  the  forms  stick,  they  can  generally 
be  started  by  tapping  them  lightly  with  a  hammer;  this  applies  as 
well  to  the  stove  pipe  cores.  Scrape  the  form  carefully,  re-oil, 
attach  the  long  side  and  they  are  ready  for  a  second  filling." 

Cisterns,  Cess-Pools. — Concrete  cisterns  and  cess-pools  are  of 
similar  construction.     "Make  a  circular  excavation  16  inches  wider 

[336] 


The  Utility  of  Concrete  on  the  Farm 

than  the  desired  diameter  of  the  cistern,  or  allow  for  a  wall  two- 
thirds  the  thickness  of  a  brick  wall  that  would  be  used  for  the  same 
purpose,  and  from  14  to  16  feet  deep.  Make  a  cylindrical  inner 
form  the  outside  diameter  of  which  shall  be  the  diameter  of  the 
cistern.  The  form  should  be  about  9  feet  long  for  a  1 4-foot  hole, 
and  ii  feet  long  for  one  16  feet  deep.  Saw  the  form  lengthwise  into 
equal  parts  for  convenience  in  handling.  Lower  the  sections  into 
the  cistern  and  there  unite  them  to  form  a  circle,  blocking  up  at 
intervals  six  inches  above  the  bottom  of  excavation.  (Withdraw 
blocking  after  filling  in  spaces  between  with  concrete  and  then  fill 
holes  left  by  blocking  with  rich  mortar.)  Make  concrete  of  one 
part  Portland  cement,  two  parts  clean,  coarse  sand,  and  four  parts 
broken  stone  or  gravel.  Mix  just  soft  enough  to  pour.  Fill  in 
space  between  the  form  and  the  earth  with  concrete,  and  puddle  it 
to  prevent  the  formation  of  stone  pockets,  using  a  long  scantling 
for  the  purpose  and  also  a  long-handled  paddle  for  working  between 
the  concrete  and  the  form.  To  construct  the  dome  without  using 
an  expensive  form,  proceed  as  follows:  Across  top  of  the  form 
build  a  floor,  leaving  a  hole  in  the  centre  two  feet  square.  Brace 
the  floor  well  with  wooden  posts  resting  on  the  bottom  of  the  cistern. 
Around  the  edges  of  hole,  and  resting  on  the  floor  described,  con- 
struct a  vertical  form  extending  up  to  the  level  of  the  ground. 

"Build  a  cone-shaped  mould  of  very  fine  wet  sand  from  the 
outer  edge  of  the  flooring  to  the  top  of  the  form  around  the  square 
hole  and  smooth  with  wooden  float.  Place  a  layer  of  concrete  four 
inches  thick  over  the  sand  so  that  the  edge  will  rest  on  the  side  wall. 

"  Let  the  concrete  set  for  a  week,  then  remove  one  of  the  floor 
boards  and  let  the  sand  fall  gradually  to  the  bottom  of  the  cistern. 
When  all  boards  and  forms  are  removed  they  can  be  easily  passed 
through  the  two-foot  aperture  and  the  sand  taken  out  of  the  cistern 
by  means  of  a  pail  lowered  with  a  rope.  This  does  away  with  all 
expensive  forms  and  is  perfectly  feasible.  The  bottom  of  the 
cistern  should  be  built  at  the  same  time  as  the  side  walls  and  should 
be  of  the  same  mixture,  six  inches  thick. " 

Box  Stalls. — Box  stalls  of  concrete  are  found  to  be  warmer  in 
winter  and  cooler  in  summer  and  so  are  held  in  high  favor.  Con- 
crete barns  with  hollow  walls  are  readily  ventilated  by  utilizing  the 
air  spaces  for  that  purpose. 

22  [337] 


Handbook  for  Cement  and  Concrete  Users 

Dairy. — The  sanitary  features  of  concrete  make  it  an  especially 
appropriate  material  for  use  in  dairy  construction.  Being  a  non- 
conductor of  heat  concrete  can  be  used  to  advantage  when  it  is 
desired  to  build  an  ice  box  as  a  part  of  the  building  itself. 

Concrete  Silos. — During  the  past  decade  silos  have  come  into 
universal  use  upon  the  American  farm.  A  good  silo  must  be  air- 
tight, water-tight,  smooth  on  the  inside,  and  maintain  an  even 
temperature.  A  concrete  silo  meets  all  these  requirements  with  the 
additional  advantage  of  being  vermin-proof  and  indestructible. 
There  are  three  kinds  of  concrete  silos,  Solid  .Wall  Monolithic, 
Hollow  Wall  Monolithic,  and  Concrete  Block.  The  first  type  re- 
qi4res  the  least  material,  the  second  prevents  freezing  of  silage  in 


FIG.  112. — Handy  Road  Roller  of  Concrete. 

cold  climates,  the  third  requires  no  forms  to  build.  The  relative 
cost  will  depend  largely  upon  local  conditions.  Having  selected 
the  type  of  silo  to  build,  the  size  is  next  considered. 

The  diameter  of  the  silo  depends  upon  the  number  of  cattle 
to  be  fed  daily,  the  height  upon  the  number  of  days  for  which  a 
supply  of  fodder  is  required.  Ten  head  of  cattle  will  consume 
thirty-six  tons  of  silage  in  180  days,  requiring  a  silo  of  10  feet  in 
diameter  and  a  height  of  25  feet. 

Seventy  head  will  consume  252  tons  in  the  same  time  and 
require  a  silo  19  feet  in  diameter  and  40  feet  high.  Intermediate 
dimensions  may  be  estimated  proportionally.  These  figures  pro- 
vide for  40  Ibs.  per  cow  per  day,  at  least  two  inches  in  depth  of 
silage  being  consumed  daily.  The  diameter  of  a  silo  should  never 
exceed  20  feet,  and  is  better  too  small  than  too  large. 

[338] 


The  Utility  of  Concrete  on  the  Farm 

"The  concrete-block  silo  is  built  of  circular  hollow  blocks  laid 
in  cement  mortar,  and  reinforced  with  steel  hoops  which  fit  in 
between  every  second  or  third  course.  When  finished  the  silo  is 
usually  painted  both  inside  and  out  with  a  cement  mortar  to  insure 
air  tightness.  The  block  silo,  like  the  hollow  silo,  has  a  dead  air 
space  in  the  walls  which  tends  to  prevent  freezing.  The  principal 
advantage  of  the  concrete-block  silo  lies  in  the  ease  with  which  it  can 
be  constructed. 

"The  hollow  wall  monolithic  concrete  silo  is  constructed  much 
the  same  as  the  solid  wall  except  that  two  walls  are  built  instead  of 


FIG.  113. — Wooden  Form  for  Concrete  Roller. 

one  with  an  air  space  of  4"  between  them.  The  inner  wall  is  rein- 
forced." The  only  reason  for  the  outer  wall  is  to  form  the  air  space 
which  prevents  the  silage  from  freezing. 

The  solid -wall  silo  is  cheap  and  easily  built  and  fulfills  all  the 
requirements  of  a  perfect  silo.  This  type  is  the  one  most  frequently 
adopted.  Its  cost  is  about  25  per  cent  less  than  hollow-wall  con- 
struction. 

The  average  dimensions  of  a  silo  are  10  feet  inside  diameter 
and  25  feet  in  height.  It  is  built  in  the  following  manner:  Ex- 
cavate to  a  depth  of  4  or  5  feet  and  dig  a  circular  trench  one  foot 
deeper  for  the  foundation  walls.  Fill  the  trench  with  a  i :  3 :  6  mix- 

[339] 


Handbook  for  Cement  and  Concrete  Users 

ture  and  spread  4  inches  more  over  the  entire  foundation.  The 
earth  under  the  footing  should  be  dry  and  firm  and  the  excavation 
well  drained.  If  the  foundation  is  poor  the  concrete  base  should 
be  reinforced  in  the  same  manner  as  the  walls.  After  the  founda- 
tion and  floor  are  complete,  the  remaining  operations  take  the  fol- 
lowing order: 


FIG.  114. — Forms  and  Staging  for  Concrete  Silos. 

1.  The  building  and  petting  of  forms. 

2.  The  placing  of  the  reinforcement. 

3.  The  mixing  and  placing  of  concrete. 

4.  The  removal,  hoisting,  and  resetting  of  the  forms. 

The  wall  forms  are  circular  and  are  placed  six  inches  apart  to 
give  the  proper  thickness  to  the  wall.  Their  height  is  generally 
three  feet,  which  enables  three  feet  of  silo  to  be  built  without  shifting 
the  forms.  After  each  three-foot  section  is  complete  the  forms 

[34o] 


The  Utility  of  Concrete  on  the  Farm 

are  loosened  by  means  of  adjusting  bolts,  raised  by  levers  and 
reset  by  the  bolts,  this  operation  being  repeated  until  the  structure 
is  complete.  The  forms  consist  of  2"  X  6"  plank  cut  circular  and 
held  together  by  i"  X  4"  cleats,  forming  2  complete  circles  held 
apart  by  i"  X  4"  studding.  The  inside  surface  is  then  covered 
with  sheet  steel,  No.  24  gauge  or  with  i"  tongued  and  grooved 
boards.  Both  outside  and  inside  forms  are  constructed  in  the  same 
manner.  Screw  bolts  are  used  to  pull  together  and  separate  the 
forms. 

Reinforcement  for  Silos. — "The  concrete  reinforcing  of  the  silo 
walls  with  small  steel  bars  or  steel  wire  must  be  done  with  accuracy 
and  care,  as  the  strength  of  the  silo  depends  on  the  correct  use  of 
steel  in  the  walls.  The  silo  walls  are  reinforced  in  two  directions; 
vertically,  to  prevent  failure  due  to  wind  pressures,  and  horizontally 
to  prevent  failure  due  to  the  pressure  of  the  silage.  Silage  is  a 
heavy  material  and  is  estimated  by  the  various  State  experimental 
stations  to  exert  a  side  pressure  of  no  Ibs.  per  square  foot  for  every 
foot  in  depth. 

' '  Since  the  pressure  in  a  silo  increases  with  the  depth,  it  is  neces- 
sary to  make  the  walls  much  stronger  at  the  bottom  than  at  the 
top. 

"In  no  case  should  the  horizontal  wires  or  bars  be  placed  over 
18"  apart  or  the  vertical  more  than  36"  apart.  The  horizontal 
reinforcement  should  be  cut  in  one  length,  if  wire,  and  the  ends 
looped  together  and  twisted  back.  If  bars  are  used,  the  ends  should 
be  bent  around  each  other  at  each  lap.  The  extreme  ends  of  the 
vertical  reinforcement  should  be  tied  by  bending  around  four  extra 
strands  of  the  largest  wire  used,  two  wires  being  placed  2" 
below  the  top  of  the  silo  wall,  and  the  other  two  in  the  centre  of  the 
silo  footings. 

"The  vertical  rods  should  be  placed  in  short  lengths,  as  it  is 
very  hard  to  handle  the  forms  with  rods  running  the  entire  height  of 
the  silo.  These  short  lengths  can  be  twisted  or  spljced  together,  as 
the  wall  is  built  up. 

"In  starting  the  vertical  reinforcement  in  the  footing  use  only 
2'  6"  or  3'  o"  lengths,  taking  six  inches  to  twist  around  the  two 
horizontal  tie  rods  or  wires  placed  in  the  centre  of  the  footings. 
This  will  leave  i'  6"  to  2'  o"  to  stick  above  the  finished  footings. 

[34i] 


Handbook  for  Cement  and  Concrete  Users 


"The  next  section  of  vertical  reinforcement  is  tied  to  these  short 
lengths,  and  they  will  not  interfere  with  the  setting  of  the  concrete 
forms." 

A  roof  should  be  made  of  2"  X  6"  rafters  set  at  a  good  pitch, 
and  covered  with  i"  sheeting;  this  in  turn  may  be  covered  with 
galvanized  iron,  tin,  or  shingles.  A  hollow-wall  silo  is  constructed 
in  the  same  way,  except  that  the  forms  are  placed  one  foot  apart  and 
circular  boxes  used  to  form  the  air  space  as  the  concrete  is  placed. 

TABLE  XXXV. — DATA  FOR  REINFORCED-CONCRETE  SILOS. 

(Including  6-inch  Floor.) 


Height. 

Inside 
Diameter. 

Thickness 
of  Wall. 

HORIZONTAL 
REINFORCEMENT. 

Cement, 
i    Part. 

Sand, 
2  Parts. 

Stone  or 
Gravel, 
4  Parts. 

Size. 

Spacing 

Feet. 

Feet. 

Inches. 

Inches. 

Inches. 

Bbl. 

Cu.  Yd. 

Cu.  Yd. 

10 

5 

6 

y< 

12 

6y2 

2 

4 

10 

10 

6 

X 

12 

15  y2 

4 

8 

15 

5 

6 

% 

12 

gy2 

3 

6 

15 

8 

6 

H 

12 

i$X 

4 

8 

15 

12 

6 

H 

12 

24 

6ya 

13 

20 

8 

6 

H 

12 

19  X 

5 

10 

2O 

12 

6 

H 

12 

29  y» 

8 

16 

2O 

15 

6 

X 

12 

38 

10 

20 

25 

10 

6 

x 

12 

27  y* 

7  X 

15 

25 

15 

6 

X 

12 

45 

12 

24 

25 

20 

6 

% 

12 

62 

i6y2 

33 

3° 

IO 

7 

X 

12 

37 

IO 

20 

3° 

15 

7 

X 

12 

58 

15* 

31 

30 

2O 

7 

y* 

12 

80 

22  ya 

45 

40 

15 

8 

% 

12 

80 

22  y, 

45 

40 

2O 

8 

H 

12 

114 

30  x 

61 

40 

25 

8 

K 

12 

147 

38  M 

77 

Place  vertical  rods  same  size  as  horizontal,  2  M  feet  apart. 

A  cubic  yard  is  about  i  K  single  load  or  K  of  a  double  load. 

Concrete  is  also  found  in  many  other  useful  forms  upon  the 
farm,  such  as:  well  curbs,  ice-houses,  root  and  mushroom  cellars, 
hen  houses,  green  houses,  flower  boxes,  cold  frames,  wind  mill 
foundations,  lawn  rollers,  porch  steps  and  lattice,  and  chimney 
caps.  Convenient  uses  for  concrete  in  such  domestic  construction 
will  occur  to  the  builder's  mind  as  necessity  arises. 

[342] 


The  Utility  of  Concrete  on  the  Farm 

Useful  Hints  for  the  Farmer. — i.  Always  use  the  best  Portland 
Cement  obtainable. 

2.  Store  your  supply  of  cement  in  a  dry  place  until  ready  to  use. 

3.  Use  sand  that  is  both  clean  and  well-graded.     A  large  pro- 
portion of  the  grains  should  measure  from  1/32  to  1/4  of  an  inch 
in  diameter.     If  fine  sand  must  be  used,  increase  the  amount  of 
cement ;  that  is,  use  a  richer  mixture. 

4.  If  the  sand  is  dirty,  wash  it. 

5.  If  the  gravel  is  dirty,  wash  it. 

6.  Before  using  the  product  of  a  gravel  bank,  screen  through  a 
i /4-inch  sieve  and  remix,  using  about  twice  as  much  stone  as  sand. 

7.  Use  gravel  or  broken  stone  up  to  2  1/2  inches  in  diameter  for 
foundations  and  thick  walls  but  limit  the  size  to  3/4  inch  diameter 
when  reinforcement  is  to  be  used. 

8.  Avoid  the  use  of  soft  stones  in  the  aggregate. 

9.  Use  clean  water,  free  from  alkalis. 

10.  Use  enough  water  to  give  the  concrete  the  consistency  of 
heavy  cream. 

1 1 .  For  ordinary  work  use  a  i  :  2  :  4  mix. 

12.  For  forms,  use  white  pine,  fir,  yellow  pine,  or  spruce  and 
green  timber  if  possible. 

13.  Grease  the  inside  of  the  forms  with  soap,  linseed  oil,  lard, 
and  kerosene,  or  petroleum. 

14.  Omit  the  greasing  if  the  surface  of  the  concrete  is  to  be  plas- 
tered, in  which  case,  wet  the  forms  just  before  placing  the  concrete. 

15.  Lay  sheathing  or  form  boards  horizontally.     Place  studs 
2  ft.  apart  for  i  in.  sheathing  and  5  ft.  apart  for  2  in.  sheathing. 

1 6.  Brace  the  forms  securely. 

17.  Do  not  drive  the  nails  all  the  way  home,  but  let  the  heads 
project  so  that  they  may  easily  be  withdrawn. 

1 8.  Keep  forms  from  bulging  or  separating  by  the  use  of  bolts 
or  wire. 

19.  Place  concrete  in  forms  in  layers  from  6  to  12  inches  thick. 
Spade  and  tamp. 

20.  After  removing  the  forms,  concrete  which  is  exposed  to  the 
sun  should  be  soaked  with  water  each  day  for  a  couple  of  weeks. 

21.  In  laying  the  concrete  in  hot  or  freezing  weather,  use  the 
precautions  outlined  in  Chapter  VII. 

[343] 


SECTION  VI 

IMPORTANT  MISCELLANEOUS  DATA 
ON  CONCRETE   CONSTRUCTION 


CHAPTER  XXX 

THE  WATERPROOFING  OF  CONCRETE  STRUCTURES 

The  Necessity  for  Waterproofing. — Modern  Methods  of  Waterproofing. — General 
Conditions  of  the  Work. — Principles  to  be  Followed. — The  Membrane  Method  in 
Detail. — The  Integral  Method  in  Detail.— Waterproofing  by  Means  of  Surface 
Coatings. — Tabular  Outline  of  Modern  Waterproofing  Processes. 

The  Necessity  for  Waterproofing. — In  many  of  the  forms  of 
construction  work  to  which  concrete  is  so  admirably  adapted,  its 
use  brings  with  it  one  inherent  fault — a  fault  for  which  remedies 
have  long  been  sought,  but  which,  until  recent  years,  have  not  been 
found  in  a  practical  form  suited  to  all  the  varied  needs  of  modern 
construction.  This  striking  fault  of  concrete  work  is  its  great  thirst 
for  water,  a  fault  which  varies  in  its  gravity  according  to  the  propor- 
tioning and  mixing  of  materials  and  to  the  nature  of  the  structure, 
it  frequently  being  the  cause  of  extremely  serious  difficulty.  Of  all 
the  opposing  forces  which  constructors  have  had  to  combat  from  time 
immemorial,  none  has  exceeded  in  its  power  for  evil  the  unwelcome 
intrusion  of  water,  and  building  materials  which  in  their  nature 
favor  such  intrusion  must  suffer  in  value  to  the  extent  of  their  per- 
meability or  absorptive  power. 

The  fact  that  in  practice,  concrete  is  frequently  found  to  be 
porous  and  permeable  has  been  one  of  the  leading  checks  in  its 
rapid  development.  Volumes  have  been  written  on  how  the  in- 
gredients might  be  mixed  to  produce  a  watertight  concrete,  but  we 
might  as  well  seek  to  solve  the  problem  of  perpetual  motion  as  to 
try  to  mix  cement,  sand,  and  stone  so  as  not  to  absorb  water. 

[344] 


The  Waterproofing  of  Concrete  Structures 

If  we  could  examine  a  section  of  concrete  under  a  powerful 
microscope,  it  would  appear  to  us  like  an  immense  sieve  through 
which  fine  particles  of  water  flow  with  more  or  less  freedom. 

We  have  seen  water  rise  up  through  concrete  walls  for  many 
feet,  and  it  will  rise  until  the  weight  of  the  water  absorbed  is  equal 
to  the  capillary  attracting  force. 

As  already  stated  in  Chapter  VII,  if  concrete  is  mixed  rich  and 
mixed  wet,  a  high  degree  of  impermeability  can  be  secured.  Mixing 
rich  imposes  greater  barriers  to  the  passage  of  water;  mixing  wet 
minimizes  the  formation  of  blowholes  by  displacing  much  of  the 
extrained  air,  but  neither  mixing  rich  nor  mixing  wet  destroys  the 
"capillary  positive"  property  of  the  concrete  mass.  Its  absorptive 
capacity  has  been  largely  decreased,  but  its  attraction  for  moisture 
has,  however,  not  been  eliminated;  thus  the  water-tightness  secured 
by  rich  and  wet  mixtures,  however  theoretically  correct  the  propor- 
tions might  be,  is  one  of  degree  only,  a  degree  sometimes  approach- 
ing ideal  but  never  reaching  it.  We  cannot  expect  that  a  'mixture 
made  of  cement  and  stone,  each  of  which  is  in  itself  "  capillary 
positive,"  or  water-attracting,  can  become  absolutely  proof  against 
the  absorption  of  water  by  the  mere  act  of  mixing,  unless,  indeed, 
the  operation  had  produced  some  phenomenal  change  in  the  very 
nature  of  the  constituent  materials.  By  care  and  diligence,  a 
mixture  may  be  produced  which  is  sufficiently  close-grained  to 
prevent  the  free  transmission  of  water,  prevent  it  sufficiently,  in 
fact,  to  be  all  that  is  required  in  many  forms  of  construction  work. 
But  where  water  absorption,  besides  water  penetration,  is  to  be 
absolutely  prevented,  no  degree  of  mixing,  no  richness  of  mixture, 
will  altogether  answer  the  purpose;  and  yet  in  many  of  the  forms 
in  which  concrete  enters  our  modern  buildings,  it  is  resistance  to 
water  absorption  that  is  required.  Not  merely  water-tightness  in 
the  ordinary  sense  of  the  word,  but  resistance  to  the  ceaseless  en- 
deavors of  atmospheric  moisture  to  find  its  way  by  capillarity  through 
porous  bodies.  Some  counteracting  influence  to  this  tendency  of 
ordinary  concrete  to  take  up  water  by  capillarity,  is,  therefore  what 
is  required  when  dampness  is  to  be  eliminated. 

It  is  true  that  concrete  exposed  to  the  free  passage  of  water  be- 
comes after  a  time  so  clogged  up  by  fine  silt  present  in  the  water 
that  the  permeability  is  greatly  reduced;  and  Hagloch  states  that 

[345] 


Handbook  for  Cement  and  Concrete  Users 

concrete-block  buildings  exposed  to  the  weather  become  water- 
tight in  from  three  to  twelve  years,  a  fact  which  we  must  likewise 
ascribe  to  the  clogging  of  the  surface  of  the  blocks  by  atmospheric 
dust  deposited  by  rain,  and  which  remains  after  evaporation. 

Modern  engineering  or  architectural  practice  should  certainly 
not  sanction  a  practice  of  waiting  for  the  erratic  and  uncertain  hand 
of  time  where  it  is  essential  to  secure  water-tightness  and  damp- 
proofness  in  concrete  structures,  and  in  the  meantime  to  incur  the 
annoying  consequences  that  always  accompany  damp  and  leaky 
structures;  and  yet  this  is  precisely  what  is  being  done  in  numberless 
instances  by  those  who  refuse  to  realize  the  importance  of  water- 
tightness  in  concrete  work,  or  while  realizing  it,  are  willing  through 
motives  of  false  economy,  to  gamble  with  the  future — nearly  always 
at  their  loss. 

The  number  of  mistakes  made  by  inadequate  provision  for 
waterproofing,  and  their  costly  consequences,  running  into  thou- 
sands of  dollars,  should  serve  as  object-lessons  to  those  who  have 
the  design  of  concrete  work  in  hand  and  the  same  degree  of  attention 
and  study  should  be  given  the  subject  of  water-tightness  as  that 
given  to  other  details  of  construction. 

The  importance  of  the  subject  and  the  scarcity  of  literature 
concerning  it  has  induced  the  author  to  cover  the  subject  in  greater 
detail  than  would  otherwise  be  necessary.* 

Method  of  Conducting  the  Work. — Work  Under  Contract. — 
Waterproofing  work  should  be  done,  if  possible,  under  contract  by 
a  specially  skilled  waterproofer,  or  by  the  concern  making  or  supply- 
ing the  material. 

In  a  large  proportion  of  cases,  the  actual  construction  is  left 
largely  to  a  contractor,  sometimes  under  a  more  or  less  loose  guaran- 
tee; often  under  no  guarantee  at  all,  and  frequently  without  the 
least  supervision  being  exercised  on  the  part  of  the  owner.  In  case 
of  trouble  after  the  completion  of  the  work,  the  owner  may  consider 
himself  fortunate  if  he  happens  to  have  a  guarantee  from  a  respon- 
sible contractor  who  values  his  reputation  for  good  work  as  much  as 
he  does  the  cost  of  remedying  the  trouble.  It  is  usually  not  a  difficult 

*  Much  of  this  chapter  has  already  appeared  under  authorship  of  Myron  H. 
Lewis  in  Cement  Era  for  1909-1910,  at  whose  special  request  the  material  was  pre- 
pared and  is  here  rearranged  with  their  permission. 

[346] 


The  Waterproofing  of  Concrete  Structures 

matter  for  a  contractor  to  disclaim  responsibility  and  endeavor  to 
shift  the  burden,  particularly  where  the  cause  of  the  difficulty  cannot 
readily  be  ascertained,  and  where  several  independent  contractors 
were  at  work  on  various  parts  of  the  job  at  the  same  time.  Any 
interference  or  injury  to  the  waterproofing  by  any  but  his  own  men, 
and  without  his  knowledge,  will  naturally  tend  to  absolve  the  water- 
proofer  from  direct  responsibility. 

Any  deviation  from  the  plans  and  specifications  forming  the 
basis  of  the  contract,  failure  to  lay  protecting  masonry  when  re- 
quired, necessary  openings  made  for  pipe  passages  through  walls 
without  the  knowledge  of  the  waterproofer,  will  likewise  relieve  the 
latter  from  his  contract  in  case  of  future  trouble.  This  division  of 
responsibility  has  often  been  the  cause  of  endless  annoyance,  delays, 
and  expensive  litigation.  A  competent  inspector  who  would  look 
after  all  the  details  of  the  waterproofing  from  the  time  preparation  of 
the  surfaces  begin  until  final  completion  of  the  work,  would  avoid  a 
great  deal  of  such  trouble.  If  a  record  is  kept  of  all  the  work  as  it 
progresses,  the  responsibility  for  any  future  trouble  may  then  be 
traced  with  some  degree  of  certainty.  Without  such  record,  which 
is  more  often  omitted  than  kept,  establishment  of  direct  responsi- 
bility is  a  difficult  matter. 

Work  Not  Under  Contract. — A  great  deal  of  waterproofing 
and  dampproofing  work  must  of  necessity  be  done,  not  by  con- 
tract, but  by  the  purchase  of  materials  and  using  same  accord- 
ing to  directions.  Where  the  work  to  be  done  is  not  large,  and 
where  the  services  of  an  experienced  waterproofer  are  not 
available,  this  method  must  be  employed,  although,  as  a  rule,  it 
is  not  so  advisable  as  having  the  work  done  by  contract,  owing 
to  the  unfamiliarity  of  the  purchaser  with  the  material  and  method 
of  application. 

In  all  waterproofing  work  a  great  deal  of  judgment  and  patience 
must  be  exercised  if  good  results  are  to  be  obtained,  and  where 
materials  are  not  applied  by  the  manufacturer  or  by  one  specially 
familiar  with  same,  the  purchaser  or  owner  should  see  that  the 
material  purchased  is  delivered,  and  that  it  be  used  in  accordance 
with  full  and  explicit  directions  furnished  by  the  manufacturer 
or  dealer.  Conditions  on  different  jobs  of  waterproofing  vary 
so  much  that  the  trade  literature  accompanying  materials  can- 

[347] 


Handbook  for  Cement  and  Concrete  Users 

not  be  expected  to  give  sufficient  information  to  cover  all  con- 
ditions, and  consequently  the  purchaser  in  ordering  material 
should  describe  to  the  dealer  in  detail  the  character  of  the 
waterproofing  work  he  has  in  hand,  and  request  that  material 
and  directions  be  sent  specially  adapted  to  that  particular  work. 
The  usual  vagueness  and  indefiniteness  of  such  descriptions  always 
gives  rise  to  unnecessary  delays,  errors  in  shipments,  and  often  in 
failure  of  the  work. 

Importance  of  Adequate  Inspection. — Thorough  inspection  is 
particularly  essential  in  the  bituminous  shield  or  membrane  method, 
where  the  waterproofing  is  to  be  covered  or  backed  up  by  protecting 
masonry  or  other  material,  and  thus  cannot  be  readily  reached  for 
repairs.  In  dampproofing  exposed  walls  of  buildings  by  application 
of  an  asphaltic  coating  on  the  interior  surface  of  the  walls,  inspection 
should  also  be  particularly  rigid  as  failure  means  the  removal  of 
the  plaster  covering.  Furthermore,  the  difficulty  in  tracing  sources 
of  leakage  when  the  waterproofing  is  covered  up  makes  the  repair 
work  more  uncertain  and  costly. 

On  large  works  particularly,  materials  specified  for  waterproofing 
purposes  should  be  subject  to  the  same  degree  of  inspection  and 
tests  as  other  construction  materials.  There  is  nothing  easier  than 
the  substitution  of  poor  materials  for  good  ones  by  irresponsible 
contractors  or  dealers,  particularly  when  the  price  is  much  below 
the  standard  price  for  like  materials.  So  many  of  the  coal  tar  and 
asphaltic  preparations  look  alike,  that  the  quality  of  the  material 
delivered  can  be  ascertained  only  by  subjecting  them  to  specified 
tests,  fixed  according  to  the  character  of  the  work  in  hand.  Water- 
proofing felts  and  other  fabrics  should  also  be  examined  for  defects, 
and  powders  and  other  materials  to  be  introduced  as  a  part  of  con- 
crete work  should  be  tested  and  compared  with  samples  obtained, 
to  see  that  the  material  ordered  is  actually  delivered. 

So  many  instances  of  failures  due  to  various  causes  have  occurred 
that  it  might  be  well  before  proceeding  to  the  detailed  consideration 
of  various  systems  of  waterproofing,  to  review  briefly  the  important 
points  'to  be  considered  in  general  to  obtain  permanency  and 
efficiency. 

The  following  general  principles,  if  carefully  followed,  will 
result  in  an  economical,  durable,  and  efficient  work: 

[348] 


The  Waterproofing  of  Concrete  Structures 


GENERAL    PRINCIPLES    TO    BE    FOLLOWED    IN    ALL 
WATERPROOFING 

i  st.  In  deciding  upon  a  system  of  waterproofing  for  any  par- 
ticular structure,  study  the  individual  conditions  of  the  problem  in 
hand.  Consider  the  location,  climate,  service,  nature  of  soil,  founda- 
tion, and  all  other  pertinent  data  and  adopt  a  plan  best  suited  for 
the  necessities  of  the  case.  The  "Tabular  Outline"  at  the  end  of 
this  chapter  will  materially  assist  in  deciding  on  the  method  to 
employ  under  given  conditions. 

2nd.  The  portions  of  the  structure  to  be  treated  must  be  so 
designed  and  prepared  that  the  waterproofing  may  be  properly 
applied  thereon;  allowing  sufficient  working  room  for  securing  good 
surfaces  and  providing  for  adequate  drainage  where  water  pressure 
is  to  be  taken  care  of  during  construction. 

3rd.  Complete,  unbroken  continuity  of  the  waterproofing 
stratum  must  be  obtained,  being  allowed  for  in  the  design  and  in- 
sisted upon  in  the  construction.  Any  breaks  in  the  continuity  of 
the  work  will  surely  be  disclosed  in  time  by  leaks. 

4th.  The  material  as  well  as  the  design  should  be  suited  to  the 
individual  conditions  of  the  work,  and  the  delivery  of  the  material 
ordered  should  be  proved  by  tests  and  comparison  with  samples 
previously  submitted. 

5th.  Where  the  designer  or  owner  is  not  .familiar  with  this  class 
of  work,  alternative  plans  and  estimates  may  be  called  for  from 
several  responsible  concerns  and  submitted  to  an  impartial  architect 
or  engineer  qualified  to  pass  judgment  on  same. 

6th.  Where  work  is  to  be  done  by  the  immediate  purchaser  of 
materials,  complete  and  explicit  instructions  should  be  obtained 
from  the  dealer  upon  written  request  and  in  conformity  with  the 
conditions  outlined  by  the  purchaser,  and  these  instructions  should 
be  rigidly  followed. 

7th.  The  labor  employed  in  all  waterproofing  work  should  be 
intelligent  and  careful  and  wherever  possible  experienced.  The 
most  satisfactory  way  is  to  have  materials  applied  by  a  representa- 
tive of  the  manufacturer  under  a  guarantee  and  under  supervision 
of  a  competent  inspector. 

[349] 


L      Handbook  for  Cement  and  Concrete  Users 

8th.  On  all  large  jobs  a  competent  inspector  should  be  present 
from  the  inception  of  the  work  to  its  completion,  and  nothing  should 
be  done,  and  no  tampering  or  interference  allowed  without  his 
knowledge. 

MODERN  METHODS  OF  WATERPROOFING 

Numerous  methods  and  materials  are  now  available  to  keep 
water  and  dampness  out  of  almost  any  structure,  and  under  the 
most  trying  conditions,  and  failure  to  secure  water-tightness  at  this 
date  must  be  looked  upon  as  a  mistake  on  the  part  of  some  one; 
either  the  designer,  constructor,  or  inspector. 

All  the  methods  may,  however,  be  embraced  in  three  general 
classes,  as  follows : 

1.  The  "Membrane"  or  " Elastic"  method;   a  term  introduced 
by  E.  W.  DeKnight.     (See  page  350.) 

2.  The  "Integral"  or  Rigid,  a  term  introduced    by  Myron  H. 
Lewis,  in  1907,  while  editing  the  Waterproofing  Magazine.     Both 
of  these  terms  have  since  been  widely  accepted  by  leading  writers 
on  the  subject.     (See  p.  359.) 

3.  Surface  Coating.     (See  p.  366.) 

These  methods  are  defined  in  detail  in  the  treatment  which 
follows : 

THE  MEMBRANE  METHOD  OF  WATERPROOFING 

The  term  "membrane  method,"  as  employed  by  De  Knight, 
refers  to  an  elastic,  continuous,  bituminous,  impervious  sheet  or 
membrane  which  completely  surrounds  the  structure  to  be  water- 
proofed. This  method  is  adapted  principally  to  waterproofing 
structures  in  course  of  erection,  particularly  those  portions  below 
ground,  such  as  subways,  tunnels,  building-foundations,  retaining- 
walls,  arches,  reservoirs,  etc.  It  is  not  so  well  adapted  to  water- 
proofing structures  already  erected,  or  to  remedy  leaky  conditions 
in  same,  or  to  damp-proofing  exposed  walls  of  superstructures. 
Other  methods  must  be  adopted  for  these  conditions  and  these  will 
be  considered  later. 

[350] 


The  Waterproofing  of  Concrete  Structures 


Materials. — The  materials  employed  in  the  membrane  method 
of  waterproofing  are : 

1.  Coal  tar  pitch  (applied  hot). 

2.  Commercial  asphalts  (applied  hot). 

3.  Specially    prepared    asphalts    and    compounds    sold    under 
various  trade  names  (applied  cold) . 

4.  Asphalt  mastic  (applied  hot). 

When  merely  dampness  is  to  be  excluded,  any  of  the  first  three 


"  ft- 

l»t  «W 

1 

Brick   wall                     4  inch**. 

'.  *.  ^ 

Tile    block                           4         •• 

f$ 

Waterproofing              '/»        •• 
Brick                                  4         •• 

>  * 

Concr,t.                             90 

n 

furring   .nd  pla»».r      4 
46H    - 

-*'••*. 

Ba5«mcnt  f!«vr 

*-.  -vv  , 

Ljgi 

n 

j 

i 

\<i-'.y 

& 

|| 

._,,..„.  ,=- 

1 

f  Op.n  .ump^^             . 

91 

• 

I^^P^ 

f^v;P^lt2J^y 

•^.^sz^jisx.ik,^         **rj'TsWi'**« 

FIG.  115. — Section  of  Building  Substructure,  showing  the  "Membrane"  Method  of 
Waterproofing.     (The  Waterproofing  Co.) 

named  materials  may  be  employed,  two  or  more  coats  being  put  on 
to  insure  thoroughly  covering  the  surfaces. 

When  water  is  to  be  excluded,  these  three  materials  are  employed 
as  cement  or  binders  in  conjunction  with  either  of  the  following 
fabrics : 

(a)  Tarred  felt. 

(b)  Asphalted  felt. 

(c)  Burlap  (ordinary). 

(d)  Burlap  (saturated  with  asphalt). 

(e)  Combinations  of  felt  and  burlap. 

[35i] 


Handbook  for  Cement  and   Concrete  Users 


The  cement  or  binder  acts  as  the  waterproofing  agent,  and  the 
fabric  acts  as  a  reinforcement,  in  addition  to  its  water-resisting 
properties  (when  the  fabric  is  a  saturated  material) . 

The  binding  material  and  fabrics  are  applied  in  alternate  layers, 
one  layer  of  fabric  coated  on  both  sides  with  the  binder  or  cement, 
forming  one  "ply."  The  number  of  ply  to  be  used  depends  upon 
the  local  conditions  and  the  head  of  water  to  be  resisted.  The 
following  table  gives  approximately  the  number  of  ply  required  for 
various  heads  of  water,  using  the  material  stated : 

TABLE   XXXVI.— GIVING   NUMBER  OF   PLY    OF  WATERPROOF- 
ING REQUIRED  FOR  VARYING  HEADS  OF  WATER. 


MATERIAL. 

Head  of  Water. 

Coal  Tar  and 
Felt. 

Commercial 
Asphalt  and  Felt. 

Special  Felts 
and  Compounds. 

Asphalt 
Mastic. 

0 

2 

2 

I 

X  in.  thick 

I 

3 

3 

2 

5^    "      " 

2 

4 

4 

3 

%    "      " 

6 

5. 

5 

4 

X  "    " 

8 

6 

6 

5 

*  "  " 

10 

7 

7 

6  . 

15 

8 

8 

7 

%  "     " 

20 

9 

9 

8 

3/    "        " 

For  bridges,  4-  to  7~ply,  depending  upon  character  of  traffic;   or  a 
mastic  about  i  inch  thick;  or  part  mastic  and  part  felt  and  cement. 


Completed  wort  -jeadu  for  ne*i  J 

retcfaer?        ~ ^Sec  fan 


Afo/.-  ^  Th,ctrnes5  of  Waterproofing  Exaggerated 
to  Distinguish  the  Piles 

FIG.  1 1 6. — Showing  Arrangement  of  Laps  in  6-Ply  Waterproofing. 
"  Membrane  Method." 

The  inspector  should  be  careful  to  observe  that  the  number  of 
ply  or  thickness  called  for  in  the  plans  and  specifications  is  actually 
put  into  place. 

[352] 


The  Waterproofing  of  Concrete  Structures 

Quality  of  Material.— Both  the  cementing  materials  and  the 
fabrics,  in  order  to  be  serviceable  for  waterproofing  operations,  must 
be  elastic  and  durable  and  retain  these  properties  through  the 
range  of  temperature  to  which  they  may  possibly  be  subjected  after 
being  placed  in  the  work. 

In  order  that  materials  of  the  desired  quality  be  obtained,  certain 
requirements  are  usually  outlined  in  the  specifications,  and  it  is 
incumbent  on  the  inspector  to  see  that  these  requirements  are  ful- 
filled as  far  as  it  is  within  his  power  to  do  so.  Laboratory  tests 
should  be  made  on  the  material  delivered  on  the  work  to  determine 
whether  the  physical  and  chemical  requirements  are  satisfied. 

Typical  Specifications  for  Bituminous  Materials. — The  following 
examples  illustrate  some  of  the  requirements  on  important  work. 
The  New  York  Rapid  Transit  Subway  has  this  specification: 

Coal  Tar  Pitch. — Shall  be  straight  run  pitch  which  will  soften 
at  70°  F.,  and  melt  at  100°  F.  The  distillate  oils,  distilled  from  the 
required  grade  of  pitch,  shall  have  a  specific  gravity  of  1.105. 

The  requirements  for  coal  tar  pitch  on  the  Pennsylvania-Long 
Island  Railroad  are  similar: 

Asphalt. — (a)  Must  be  best  grade  of  Bermudez,  Alcatraz,  or 
Lake  of  equal  quality. 

(b)  It  must  be  either  a  natural  asphalt  or  a  mixture  of  natural 
asphalts. 

(c)  Must  contain  in  the  refined  state  not  less  than  95  per  cent 
natural  bitumen  soluble  in  rectified  carbon  bisulphide  or  in  chloro- 
form. 

(d)  Not  less  than  two-thirds  of  the  total  bitumen  shall  be  soluble 
in  petroleum  naphtha  of  70°  Baume,  or  in  acetone. 

(e)  The  asphalt  shall  not  lose  more  than  4  per  cent  of  its  weight 
at  a  temperature  of  300°  F.,  when  maintained  for  ten  hours. 

(/)  No  injurious  ingredients  shall  be  present. 

An  excellent  set  of  requirements  for  obtaining  a  good  asphalt 
is  found  in  the  specifications  of  the  Chicago  and  Northwestern 
Railroad.  These  are  as  follows: 

1.  The   asphalt    must    be   free   from   coal  tar  or  any  of    its 
products. 

2.  Must  not  volatilize  more  than  one-half  of  one  per  cent  under 
a  temperature  of  300°  F.,  maintained  for  ten  hours. 

23  [  353  ] 


Handbook  for  Cement  and  Concrete  Users 

3.  Must  not  be  affected  by : 

A  2o-per-cent  solution  of  ammonia. 
A  25-per-cent  solution  of  sulphuric  acid. 
A  35-per-cent  solution  of  muriatic  acid. 
A  saturated  solution  of  sodium  chloride. 

4.  Must  not  show  any  hydrolitic  decomposition  when  subjected, 
for  a  period  of  ten  hours,  to  hourly  immersions  in  water  with  alter- 
nate rapid  drying  by  warm  air  currents. 

5.  Range  of  temperature: 

(a)  For  metallic  structure  exposed  to  direct  rays  of  sun. 
Flow  point  not  less  than  2 1 2°  F. 

Brittleness — Must  not  become  brittle  at  o°  F.,  when  spread  on 
thin  glass. 

(b)  For  underground  structure  such  as  masonry  arches,  abut- 
ments, retaining  walls,  building  foundations,  etc. 

Flow  point,  185°  F. 
Brittle  point,  o°  F. 

(c)  Mastic  made  from  (a)  or  (b)  must  be  pliable  at  o°  F. 

Must  not  perceptibly  indent  under  load  of  20  pounds  per  square 
inch  when  at  temperature  of  130°  F. 

6.  Preparation  of  the  asphalt. 

(a)  Care  should  be  taken  that  the  asphalt  is  not  "  pitched." 
This  will  take  place  if  heated  above  450°  F.     The  inspector  can  tell 
when  this  point  is  reached  by  the  change  in  color  of  paper  from  a 
bluish  tinge  to  a  yellowish  tinge. 

(b)  The  inspector  can  further  test  for  the  sufficiency  of  the 
cooking  by  putting  in  and  withdrawing  a  stick  of  wood.     The 
asphalt  should  cling  to  it. 

(c)  Should  pitching  occur,  fresh  material  should  at  once  be  added 
to  reduce  the  temperature. 

(d)  When  delays  occur  in  the  work  and  pitching  is  to  be  pre- 
vented, the  fire  should  be  banked  or  drawn  and  fresh  material  added 
to  reduce  the  temperature. 

The  weight  is  also  a  distinguishing  feature  between  the  various 
materials  and  will  aid  the  inspector  in  his  work.  They  are  approxi- 
mately as  follows: 

Coal  tar,  63  pounds  per  cubic  foot. 

Coal  tar  pitch,  75  pounds  per  cubic  foot. 

[354] 


The  Waterproofing  of  Concrete  Structures 

Trinidad  asphalt  (natural),  80  pounds  per  cubic  foot. 

Trinidad  asphalt  (refined),  93  pounds  per  cubic  foot. 

A  good  coal  tar  pitch  for  waterproofing  should  weigh  70  to  80 
pounds,  and  a  good  asphalt  90  to  95  pounds  per  cubic  foot. 

The  relatively  low  melting-point  will  readily  distinguish  whether 
a  coal  tar  is  being  substituted,  .when  asphalt  is  specified,  and  in 
addition  to  the  weight  and  flowing-points  the  characteristic  odor  of 
the  tar  will  detect  substitution. 

Adulteration  of  the  asphalts  with  cheaper  petroleum  products 
and  substitution  of  domestic  asphalts  for  the  Trinidad  or  other 
foreign  brand  usually  specified,  will  also  make  itself  known  in  the 
lower  flowing-point  and  lower  flaming-point,  the  petroleum  oils 
decreasing  these  points  in  accordance  with  the  amount  present. 

When  bituminous  products  are  specified  and  delivered  under 
trade  names  and  are  to  be  applied  cold,  the  flowing-point  cannot  be 
used  as  a  factor  so  readily,  but  such  material  should  also  be  tested 
for  brittleness  under  low  temperature,  and  stability  at  high  tempera- 
ture and  acid  tests  should  be  made  to  determine  their  immunity 
from  ready  attack  by  acid  present  in  the  ground  water. 

Specification  for  As  phallic  Felt. — The  felt  must  be  saturated 
and  coated  with  asphaltic  products  and  must  conform  to  the  follow- 
ing requirements : 

(a)  The  weight  per  100  sq.  ft.  shall  be  from  12  to  14  Ibs., 
saturated,  and  from  5  to  6  Ibs.  unsaturated. 

(b)  The  weight  of  the  saturation  and  coating  shall  be  from 
1.25  to  1.75  times  the  weight  of  the  unsaturated  felt  if  coated  on 
both  sides,  and  from  i  to  1.5  times  the  weight  of  the  unsaturated 
felt  if  coated  on  one  side. 

(c)  The  saturation  shall  be  complete. 

(d)  The  ash  from  the  unsaturated  felt  shall  not  exceed  5  per 
cent  by  weight. 

(e)  The  wool  in  the  unsaturated  felt  shall  not  be  less  than 
25  per  cent  by  weight. 

(/)  Soapstone  or  other  substances  in  the  surface  of  the  felt 
to  prevent  adhesion  shall  not  exceed  .5  Ib.  per  100  sq.  ft.  of  felt. 

(g)  The  saturating  and  coating  materials  shall  remain  plastic 
after  being  heated  to  250  degrees  Fahr.  during  10  hrs.  The  coating 
not  to  crack  when  the  felt  is  bent  double  at  ordinary  temperature. 

[355] 


Handbook  for  Cement  and  Concrete  Users 

(h)  The  felt  shall  be  soft,  pliable,  and  tough  when  received 
from  the  factory  and  until  placed  in  the  work. 

(i)  The  quotient  obtained  by  dividing  the  tensile  strength  in 
pounds  of  a  strip  i  in.  wide,  cut  lengthwise,  by  the  weight  in  pounds 
of  100  sq.  ft.  shall  not  be  less  than  7. 

(j)  The  quotient  obtained  by  dividing  the  tensile  strength  in 
pounds  of  a  strip  i  in.  wide,  cut  crosswise,  by  the  weight  in  pounds 
of  100  sq.  ft.  shall  not  be  less  than  3.5. 

(K)  The  strength  saturated  shall  be  at  least  25  per  cent  more 
than  the  strength  unsaturated,  taken  lengthwise. 

The  inspector  should  see  that  all  the  material  delivered  arrives 
in  unbroken  packages  and  contains  the  proper  label  of  the  manu- 
facturer as  specified. 

Application  of  Materials  in  the  Membrane  Method. — In  the 
application  of  the  materials,  certain  fundamental  requirements  must 
be  fulfilled  upon  which  the  final  success  of  the  work  will  largely 
depend,  and  it  is  the  duty  of  the  inspector  to  see  that  such  require- 
ments are  fulfilled.  These  requirements  may  be  conveniently 
classed  under  three  headings,  thus: 

1.  Preparation  of  surface. 

2.  Continuity  of  work. 

3.  Protection  of  waterproofing. 

Preparation  of  Surface. — It  is  difficult  to  make  a  bituminous 
sheet  adhere  to  a  surface  that  is  either  too  rough,  too  wet,  covered 
with  dirt  or  foreign  matter  or  possessing  too  fine  a  glaze  due  to  rich- 
ness of  cement  surface.  It  is,  therefore,  necessary  to  see  that : 

(a)  All  dirt  and  foreign  matter  are  removed  before  waterproofing 
is  applied. 

(b)  That  an  adequate  drainage  system  is  installed  and  main- 
tained, and  that  the  wall  is  dry  when    the   waterproofing   is  ap- 
plied. 

(c)  In  case  complete  dryness  cannot  be  secured,  a  layer  of  felt  in 
addition  to  those  called  for  in  the  specifications  is  first  laid  against 
the  surface. 

Some  specifications  require  that  asphalt  cut  with  naphtha  shall 
first  be  applied  cold. 

(d)  The  surface  should  be  smoothed  off  with  a  trowel,  if  toe 
rough. 

[356] 


The  Waterproofing  of  Concrete  Structures 


I  II 


(e)  In  case  wall  is  of  concrete,  that  the  concrete  be  thoroughly  set. 

(f)  In  case  wall  is  covered  with  a  fine  skin  of  cement,  see  that  it 
is  roughened  up  to  insure  sticking  of  material. 

(g)  Sharp  projections  on  the  masonry  should  be  removed  or 
they  will  puncture  the  waterproofing. 

(h)  Metal  surfaces  should  be  dry  and  clean,  free  from  rust, 
loose  scale,  and  dirt.  If  previously  coated  with  oil,  same  should  be 

removed   with   benzine  or  other 
^3     suitable   means.     Warming  may 
be  accomplished  by  heated  sand, 
which  is   removed  as  material  is  ap- 
plied. 

Continuity  of  Work. — Lack  of  con- 
tinuity will  be  fatal  to  any  waterproof- 
ing work,  as  water  is  sure  to  find  its 
way  through  any  breaks,  however 
small.  In  order  to  secure  proper  con- 
tinuity, see  that: 

(a)  The  waterproof  sheet  is  applied 
continuously  over  the  whole  surface  to 
be  treated  as  shown  on  the  plans; 
thus  in  building  substructures  it  should 
be  applied  over  all  footings,  walls, 
cellar  bottoms  and  on  the  outer  face  of  all  foundation  walls. 

(b)  That  all  joints  are  broken  properly  at  least  4  inches  on  cross 
joints  and  12  inches  on  longitudinal,  and  at  least  12  inches  lap  left  at 
corners  to  form  good  connections  with  adjoining  sections. 

(c)  Where  it  is  necessary  to  stop  work,  laps  of  at  least  1 2  inches 
should  be  provided  for  joining  on  new  work. 

(d)  Each  layer  of  pitch,  asphalt,  or  other  cementing  material 
must  completely  cover  the  surface  on  which  it  is  spread,  without 
cracks  or  blowholes  or  other  imperfections. 

(e)  The  fabric  must  be  rolled  out  smoothly  and  pressed  over 
the  cementing  material,  so  as  to  insure  its  sticking  thoroughly  and 
evenly  over  the  entire  surface. 

(/)  In  connecting  side  wall  with  floor  work,  the  layers  of  the 
fabric  on  the  sides  should  be  carried  down  on  the  outside  of  the 
ends  of  the  floor  layer  and  lap  at  least  24  inches. 

[357] 


FIG.  117. — Method  of  Water- 
proofing Retaining  Wall. 


Handbook  for  Cement  and  Concrete  Users 

(g)  In  connecting  side  wall  and  roof  work,  the  layers  of  fabric 
of  the  roof  should  be  carried  on  the  outside  of  the  sidewall  layers 
with  at  least  a  24-inch  lap. 

(h)  Before  new  work  is  added  to  old,  the  inspector  should  be 
careful  to  see  that  the  old  surface  is  cleaned  of  all  foreign  matter, 
such  as  cement,  mortar,  or  other  substance  which  finds  its  way  there- 
on. After  cleaning  the  laps,  they  must  be  well  covered  with  fresh 
cementing  material  before  new  layer  of  fabric  is  placed  against  it, 
and  the  new  fabric  should  be  made  to  stick  smoothly  and  evenly 
over  entire  joint  area. 

Protection. — After  the  waterproofing  has  been  put  into  place, 


Waterproofing 


FIG.  118. — Draining  and  Waterproofing  Tunnel  Wall. 

it  must  be  properly  protected  against  injury  from  any  cause  what- 
ever.    Such  injury  is  liable  to  occur  by  puncturing  when : 

(a)  Backfilling  with  earth. 

(b)  Depositing  concrete  against  same. 

(c)  Laying  brickwork  or  rubble  against  same. 
Lack  of  protection  may  also  cause: 

(d)  Bulging  of  waterproofing  from  wall. 

(e)  Cracking  of  same  due  to  bulging. 

(f)  Running  of  material  due  to  heat. 

(g)  Injury  due  to  frost  particularly  when  materials,  brittle  at 
low  temperatures,  are  used. 

Injury  from  any  of  the  above  causes  may  be  avoided  by  placing 

[358] 


The  Waterproofing  of  Concrete  Structures 

against  the  waterproofing  a  protecting  layer  of  cement  mortar  mixed 
in  the  proportions  of  i  part  cement  to  2  i  /  2  parts  sand. 

This  safety  coat  should  be  placed  as  soon  as  possible  after  the 
laying  of  the  waterproofing,  not  exceeding  12  to  24  hours.  Failure 
to  place  such  protection,  if  called  for  in  specifications,  will  be 
sufficient  cause  for  relieving  the  waterproofer  of  responsibility,  if 
under  a  guarantee. 

When  this  safety  coat  is  omitted,  and  backing  of  earth  or  concrete, 
brick  or  stone  masonry  is  to  be  laid  immediately  against  the  water- 
proofing, the  greatest  care  must  be  exercised  that  the  sheet  is  not 
punctured  by  sharp  corners  of  stones  or  bricks. 

When  brick  work  is  placed  against  waterproofing  on  vertical 
walls,  a  slight  space  may  be  left  for  slushing  in  with  mortar  to  avoid 
puncturing.  The  bricks  should  not  be  rammed  up  against  the 
waterproofing  sheet. 

Injury  to  the  waterproofing  might  also  occur  when  the  hydro- 
static pressure  is  very  large,  and  insufficient  weight  has  been  placed 
upon  same  to  secure  it  against  displacement  by  such  pressure. 

Protection  of  the  waterproofing  should  not  stop  with  placing 
the  backfilling  on  same.  Tampering  with  it  should  be  absolutely 
forbidden.  When  openings  or  incisions  in  the  sheet  are  necessary, 
the  inspector  should  be  notified,  and  he  must  see  that  such  places 
are  repaired  in  the  most  thorough  manner.  All  pipe  passages 
should  be  pocketed  and  connections  thoroughly  made.  Such 
places  should  not  be  covered  up  until  the  work  has  been  examined 
by  the  inspector  and  found  properly  executed. 


THE  INTEGRAL  METHOD  OF  WATERPROOFING 

The  term  " Integral"  refers  to  those  methods  wherein  the  water- 
proofing material  becomes  an  integral  part  of  the  structure  treated. 
It  includes: 

I.  The  various  methods  employed  in  making  concrete  and 
masonry  impermeable  per  se : 

By  properly  grading  the  materials  and 

(a)  The  addition    of   special  materials  to  the  water    used   in 
tempering  the  cement,  or 

(b)  The  addition  of  special  materials,  dry,  to  the  cement,  or 

[359] 


Handbook  for  Cement  and  Concrete  Users 

(c)  The  use  of  a  cement  waterproofed  in  the  process  of 
manufacture. 

II.  The  application  of  materials  thus  prepared  as  a  plaster  or 
coating  to  the  surfaces  to  be  treated,  such  coating  becoming  an 
integral  part  of  the  structure. 

The  Integral  method  is  distinguished  from  purely  surface  appli- 
cations, in  that  the  latter  are  applied  as  a  paint,  and  while  some  of 
the  materials  penetrate  to  a  considerable  extent,  periodic  renewal 
is  required  when  exposed  to  the  elements,  although,  with  some  of 
the  materials,  renewals  may  not  be  required  for  many  years. 

Adaptability  of  the  Integral  Method.— The  " Integral"  method 
of  waterproofing  as  above  outlined,  is  adapted  to  treatment  of 
numerous  conditions.  In  the  form  of  the  coating,  it  is  particularly 
adapted  to  remedying  leaky  conditions  in  substructures  already 
erected,  where  excavations  would  be  too  costly  and  inconvenient. 

Although  the  logical  place  to  apply  waterproof  cement  coatings 
is  on  surfaces  exposed  to  the  water,  yet  owing  to  the  inaccessibility 
of  the  outer  surfaces  for  examination  and  repairs,  the  coatings  are 
applied  to  the  inner  surfaces  as  shown  in  Fig.  117.  It  will  with- 
stand any  ordinary  water  pressure  in  this  position,  if  the  work 
is  properly  executed. 

In  mass  concrete  work,  imperviousness  may  be  secured,  as  al- 
ready stated,  by  the  simple  expedient  of  carefully  grading  the 
materials,  proper  mixing,  and  the  rational  use  of  reinforcement  and 
expansion  joints  to  prevent  the  development  of  cracks.  For  many 
conditions,  no  further  treatment  is  necessary.  Where,  however, 
capillary  absorption  is  to  be  prevented,  and  where  even  dampness 
or  slight  leakage  is  objectionable,  the  introduction  of  special  ma- 
terials in  the  work  is  advisable. 

In  many  cases,  either  the  Membrane  or  Integral  methods  may 
be  employed  with  equally  good  results,  and  the  selection  of  type 
must  be  made  by  the  designer,  after  comparing  their  cost. 

Addition  of  Waterproofing  Material  to  the  Concrete. — Concrete, 
even  when  mixed  according  to  the  most  rigid  rules  and  under  the 
most  competent  supervision,  often  falls  short  of  its  purpose  in 
resisting  water  penetrations.  This  condition,  and  the  inherent 
attraction  of  concrete  for  water,  has  resulted  in  the  appearance  on 
the  market  of  a  large  number  of  compounds  having  the  express 

[360] 


The  Waterproofing  of  Concrete  Structures 


purpose  of  obviating  these  objections.     The  compounds  are  of  a 
proprietary  nature,  and  the  composition  is  kept  secret  by  the  makers. 
The  designer  not  familiar  with  them  should  make  his  selection  of 
material  only  after  carefully  investigating  their  merits. 
These  compounds  may  be  grouped  in  four  classes: 
i.  Powders. — Added  dry  to  cement  before  mixing.     These  are 
usually  of  white,  floury  consistency,  extremely  fine,  and  are  water- 
repellant.     The   water-repellant   properties   are 
imparted   by  the    introduction    of    a    metallic 
stearate,  such  as  lime  soap,  which  is  of  a  fatty 
nature.      Being  so  extremely  fine,  they  have  a 
distinct  void-filling  property,  and  their  uniform 
distribution  in  the   cement  must  give  a  denser 
mixture.     In  addition  to  the  metallic  stearates, 
they  contain  varying  proportions  of  alum  and 
hydrated  lime.     The  latter  materials  are  them- 
selves extensively  used  to  densify  and  waterproof 
concrete  work. 

2.  Cements  are  now  manufactured  un- 
der several  patents,  where  by  the  addi- 
tion of  special  materials  and  special  treat- 
ment    a     water 


'  Open  or  cloatd  sump 


FIG.  119. — Section  of  Building  Substructure  showing  the 
"  Integral  "  Method  of  Waterproofing. 


repellant  cement 
is  obtained. 

3.  Liquids.  — 
Added  to  water 
employed  in  tem- 
pering the  ce- 
ment. These  are  various  forms  of  metallic  salts,  such  as  chloride 
of  lime  and  oil  emulsions.  Soap  solutions  are  also  employed  for 
this  purpose.  In  the  case  of  the  liquids,  the  waterproofing  prop- 
erty is  imparted  by  the  formation  of  gelatinous  coatings  about  the 
minute  particles  of  the  concrete.  Lime  scraps,  suspended  in  the 
water,  are  also  employed. 

4.  Combinations  of  liquids  and  powders.  The  most  frequent 
form  is  the  addition  of  alum  dry  to  the  cement,  and  the  mixture  of 
soap  solution  to  the  water  employed  in  tempering  the  cement. 
This  is  usually  referred  to  as  the  "  Sylvester"  mixture.  In  this  case 

[361] 


Handbook  for  Cement  and  Concrete  Users 

waterproofness  is  imparted  by  the  precipitation  of  insoluble  com- 
pounds in  the  voids. 

•Where  any  expensive  work  is  to  be  undertaken,  and  the  em- 
ployment of  any  of  these  compounds  is  contemplated,  tests  should 
be  carried  on  to  determine: 

1.  The  effect  on  the  strength  of  the  concrete. 

2.  Their  behavior  when  subjected  to  extreme  ranges  of  tempera- 
ture. 

3.  Their  immunity  to  decomposition  by  various    acids,    etc., 
liable  to  reach  the  concrete. 

4.  The  effect  of  admixture  of  the  materials  to  steel,  embedded  in 
concrete. 

These  materials  being  usually  purchased  under  trade  names, 
and  their  composition  being  secret,  there  is  little  that  the  inspector 
is  capable  of  doing  in  regard  to  them.  He  should,  however,  satisfy 
himself  that  the  material  specified  is  being  used  on  the  work,  by 
identifying  the  packages,  and  noting  that  they  are  unbroken,  and 
contain  the  proper  trade-marks. 

He  should  have  the  directions  furnished  by  the  manufacturer, 
see  that  they  are  explicitly  followed,  and  allow  variations  only  in  case 
unforeseen  conditions  are  encountered,  and  where  special  instructions 
to  cover  them  are  not  at  hand. 

When  the  work  is  being  done  by  the  manufacturer  or  his  repre- 
sentative under  a  guarantee  to  secure  water-tightness,  the  inspector 
should  give  the  latter  free  rein  to  follow  his  own  methods,  provid- 
ing they  are  in  conformity  with  the  general  contract.  He  should, 
however,  keep  a  complete  and  reliable  record  of  the  progress  of  the 
work  for  future  reference. 

Workmanship. — As  previously  stated,  the  treatment  may  consist 
of  adding  waterproofing  material  in  the  body  of  the  concrete,  or  in  a 
coating  or  plaster  applied  to  the  surfaces  to  be  protected. 

In  either  case  the  essential  requirements  for  good  work  are : 

1.  Homogeneity  of  mixture. 

2.  Continuity  of  work. 

3.  Soundness  or  freedom  from  cracks,  etc. 

When  applied  as  a  coating  a  further  requirement  is: 

4.  Bond. — A  uniform  and  efficient  bond  of  coating  to  concrete  or 
masonry  surface  must  be  secured. 

[362] 


The  Waterproofing  of  Concrete  Structures 

Homogeneity. — The  inspector  should  see  that  the  waterproofing 
material  is  uniformly  distributed  throughout  the  work.  Irregular 
distribution  will  result  in  weak  spots,  which  should  be  avoided  as 
much  as  possible. 

Continuity. — He  must  see  that  all  portions  called  for  on  the 


waterproofing. 

'••'<?^  &i^fc*£r:?£i'~ 


BroKen  sTone 
Concrete 


FIG.  1 20. — Details  of  Sump  Employed  in  the  Integral  Method  of  Waterproofing. 
Sump  may  be  Sealed  or  Open  as  Required. 

plans  receive  waterproofing  treatment.  Any  omissions  will  break 
the  continuity  of  the  work  and  will  nullify  the  object  which  the 
designer  had  endeavored  to  attain. 

Soundness,   Freedom  from   Cracks,   Etc. — These   are   essential 
requirements   in  successful   waterproofing  work  by  the   Integral 


FIG.  i2i.— Passing  Pipe  Through  Concrete  Wall.     Method  of  Making 
Water-tight  Joint. 

method,  and  they  should  be  minimized  by  the  use  of  expansion 
joints  and  reinforcements.  The  inspector  should  be  particularly 
careful  that  the  plans  are  properly  carried  out  in  this  respect. 

Bond. — As  already  stated,  the  bond  is  an  important  matter  where 
the  waterproofing  is  done  by  the  application  of  a  coating  of  specially 

[363] 


Handbook  for  Cement  and  Concrete  Users 

prepared  cement  mortar  to  the  concrete  or  masonry  surface.  The 
coating  should  be  homogeneous,  continuous,  sound,  and  uniform. 
A  good  bond  will  require: 

1.  Correct  mixture  of  the  coating  materials. 

2.  Proper  condition  of  surface  to  receive  the  coating. 

3.  Thoroughness  in  application. 

4.  Careful  connection  of  one  day's  work  to  preceding. 

INSTRUCTIONS     FOR     APPLYING     WATERPROOF 
CEMENT     COATINGS 

In  order  to  carry  out  the  above  provisions  the  following  directions 
are  added:  A  powdered  material  is  here  taken  as  an  example, 
although  most  of  the  directions  apply  equally  as  well  whatever 
character  of  compound  is  to  be  employed.  This  method  of  pro- 
cedure is  followed  by  some  of  the  leading  contractors  doing  this 
class  of  work,  and  if  intelligently  carried  out,  a  durable  and  water- 
tight job  will  be  secured. 

1.  Preparation  of  Coating. 

(a)  To  each  bag  of  cement  add  dry  the  waterproof  compound 
called  for  in  specifications  in  percentage  directed  by  manufacturer. 
Manipulate  until  the  appearance  and  color  indicate  that  a  uniform 
mixture  has  been  obtained. 

(b)  Mix  the  cement  thus  waterproofed  with  sand  in  proportion 
of  i  cement  to  2  sand.     Sand  to  be  absolutely  clean  and  well  graded 
from  coarse  to  fine.     Sand  need  not  be  sharp.     Sand  is  to  be 
moistened,    waterproof    cement    spread    over    it,    and    the  whole 
manipulated  until  a   homogeneous  waterproof   coating   mortar   is 
obtained. 

2.  Preparation  of  Surface. 

(a)  The  old  concrete  surface  should  be  thoroughly  chipped  not 
more  than  two  days  prior  to  application  of  the  coating.     The 
chipping  may  be  greatly  facilitated  by  a  previous  application  of 
muriatic  acid  or  a  bonding  compound,  the  strength  of  the  solution 
depending  upon  the  age  of  the  wall;    or  the  use  of  the  bonding 
material  may  be  deferred  until  the  chipping  has  been  completed. 

(b)  In  case  acid  or  bonding  powders  have  been  employed,  all 
unspent  acid  should  be  removed  by  rigid  application  of  the  hose, 

[364] 


The  Waterproofing  of  Concrete  Structures 

immediately  after  the  acid  treatment  has  reached  a  satisfactory 
stage. 

(c)  The  dust,  dirt,  and  loosened  material  must  be  completely 
removed,   either  by   patient   scrubbing   with   stiff  brushes,   water 
nozzle,  steam  jet,  or  other  suitable  means.     An  absolutely  clean 
surface  should  be  obtained,  riot  more  than  twenty-four  hours  ahead 
of  the  application  of  the  coating. 

(d)  All  holes  should  be  filled  up,  large  holes  with  the  waterproof 
concrete,  and  small  holes  with  waterproofed  mortar.     Before  filling 
the  holes,  the  old  surfaces  should  be  drenched  and  slush  coating 
applied,  as  described  below. 

(e)  Just  before  the  main  cement  coating  is  to  be  applied,  the  entire 
wall  should  be  drenched  and  soaked  to  its  full  absorbing  capacity. 

3.  Application  of  Coating. 

(a)  Before  the  wall  shows  marked  signs  of  drying  a  slush  coat- 
ing should  be  applied  quickly  and  uniformly  with  a  palmetto.     This 
slush  coating  should  be  made  by  a  thorough  mixing  of  water- 
proofed cement  in  water,  to  the  consistency  of  cream. 

(b)  Before  the  slush  coating  has  dried,  the  first  application  should 
be  applied  as  a  scratch  coat,  one-fourth  to  three-eighth  inch  thick, 
and  pressure  brought  on  the  trowel  to  push  the  coating  on,  to  form 
a  uniform  bearing.     The  scratch  coating  should  be  made  by  mixing 
one  part  of  waterproofed  cement  to  two  parts  of  clean,  well  graded 
moist  sand,  and  enough  water  to  obtain  proper  consistency. 

(c)  The  scratch  coat  should  be  trowelled  to  a  fairly  good  surface 
and  scratched  before  hardening. 

(d)  Upon  the  scratch  coat,  before  its  final  setting,  the  finishing 
coat  of  sufficient  thickness  to  obtain  a  total  thickness  of  five-eighths 
inch  should  be  applied.     This  should  be  pushed  on  hard  and 
uniformly  trowelled  and  floated  to  a  true  surface,  free  from  pin 
holes,  projections,  or  other  defects.    The  composition  of  the  finished 
coating  shall  be  one  part  waterproofed  cement  to  two  parts  sand, 
well  graded  and  previously  moistened. 

(e)  If  not  feasible  to  apply  finishing  coat  until  after  the  scratch 
coat  has  already  set,  the  latter  must  be  thoroughly  rinsed  and  slush- 
coated  before  finishing  coat  is  applied. 

(/)  The  floating  of  the  finished  surface  shall  be  done  from  the 
bottom  of  the  wall  up. 

.[365] 


Handbook  for  Cement  and  Concrete  Users 

(g)  When  the  work  has  been  completed  all  bad  and  defective 
work  shall  be  cut  out  and  replaced  in  the  same  manner  as  above 
described. 

(h)  When  the  work  has  thoroughly  hardened,  sounding  with  a 
light  hammer  over  the  wall  should  be  resorted  to,  to  discover  any 
loose  or  hollow  portions,  and  same  must  be  cut  out  and  replaced. 

(i)  In  leaving  a  portion  of  work  for  the  day,  the  section  being 
finished  should  be  left  with  straight  edges.  When  the  new  work  is 
to  be  started  the  old  edges  are  to  be  roughened  up  by  chipping  and 
roughing  with  the  trowel  and  the  same  rinsed  and  slush-coated,  as 
already  described. 

WATERPROOFING  BY  MEANS  OF  SURFACE  COATINGS 

The  third  or  "  Surf  ace  Coating"  method  remains  to  be  con- 
sidered. In  this  method,  the  materials  are  applied  as  a  paint  to 
the  surface  to  be  treated,  and  are  presumed,  upon  completion,  to 
form  a  barrier  to  the  passage  of  water. 

Applicability. — Owing  to  the  comparatively  low  cost  and  ease 
of  application,  this  method  of  waterproofing  has  been  widely 
adopted  and  often,  unfortunately,  under  conditions  where  it  had  no 
right  to  be  employed. 

It  should  not  be  employed  to  keep  water  out  of  basements  or 
substructures  of  buildings,  particularly  when  subject  to  water 
pressure;  its  function  in  building  work  being  to  damp  proof  more 
than  to  water  proof.  Its  use  under  ground  can  be  justified  only 
where  no  permanent  water  is  present  and  ground  dampness  merely 
is  to  be  kept  out.  Its  principal  uses  are: 

1.  To  keep  water  and  dampness  out  of  superstructure  of  buildings. 

2.  To  preserve  building  materials  and  structures  from  decay 
due  to  absorption  of  water  and  other  atmospheric  impurities,  and 
avoid  staining  of  stone  and  efflorescence. 

3.  To  avoid  and  remedy  leaky  conditions  in  tanks,  conduits, 
and  other  water-containing  structures. 

Materials. — A  large  variety  of  materials  is  on  the  market  for 
waterproofing  by  this  method,  but  they  may  be  all  conveniently 
included  in  five  distinct  classes.  A  large  proportion  of  them  are 
made  on  secret  formulas  and  sold  under  trade  names  and  sub- 

[366] 


The  Waterproofing  of  Concrete  Structures 

stitution  of  inferior  materials  is  often  tempting,  owing  to  the  wide 
variations  in  price. 

The  materials  employed  as  surface  coatings  may  be  grouped  in 
the  following  classes : 

1.  Soap  and  alum  mixtures  applied  in  alternate  coats,  popularly 
known  as  the  "  Sylvester"  process. 

2.  Paraffine  and  other  mineral  bases,  Applied  cold  (in  solution), 
or  paraffine  in  melted  condition. 

3.  Specially  prepared  bituminous  products. 

4.  Cement  grout,  with  or  without  the  addition  of  water  repellants. 

5.  Miscellaneous  materials  of  unknown  composition. 

All  of  the  above,  except  class  3  (bituminous  products),  are 
applied  to  the  surfaces  directly  exposed  to  the  action  of  water.  In 
the  case  of  class  3,  the  application  is  made  to  the  inner  surface  of 
exposed  building  walls,  its  function  in  this  position  being  not  only 
to  dampproof,  but  to  serve  as  an  insulating  film  against  rapid  changes 
of  temperature;  and  also  to  replace  furring  and  lathing,  as  plaster 
may  be  directly  applied  thereon.  This  is  particularly  so  in  the  case 
of  brick  walls.  Furthermore,  the  material  being  protected  from  the 
elements,  a  long  life  is  assured. 

The  Sylvester  Process. — This  process  has  been  principally  em- 
ployed and  is  mainly  adapted  to  coating  the  surfaces  of  tanks, 
conduits,  and  other  water-carrying  structures,  to  render  them  tight. 
It  has  also  been  employed  for  treating  concrete  roofs  and  walls  with 
varying  success.  The  process  consists  of  alternate  applications  of 
solutions,  the  first,  third,  etc.,  coats  of  soap,  and  the  second,  fourth, 
etc.,  of  alum. 

Proportions. — For  soap  solution — 3/4  Ib.  castile  soap  to  i  gallon 
of  water.  For  alum  solution — i  Ib.  alum  to  8  gallons  of  water. 

The  following  precautions  should  be  observed : 

1.  The  soap  and  alum  should  each  be  perfectly  dissolved  before 
using. 

2.  The  surfaces  should  be  clean  and  dry. 

3.  The  soap  solution  should  be  applied  first. 

4.  The  soap  solution  should  be  boiling  hot. 

5.  A  flat  brush  should  be  used. 

6.  Care  should  be  taken  to  avoid  frothing. 

7.  The  first  coat  to  remain  on  24  hours,  or  until  it  is  dry  and  hard. 

[367] 


Handbook  for  Cement  and  Concrete  Users 

8.  Temperature  of  air  to  be  not  less  than  50°  F.  at  time  of 
application. 

9.  Alum  solution  to  be  about  60°  to  70°  F. 

10.  Alum  solution,  second  coat  to  be  applied  thoroughly  over 
the  first  coat. 

11.  Second  coat  allowed  to  remain  24  hours  before  third  coat 
(soap  solution)  is  put  on. 

12.  Two  or  more  coats  of  each  should  be  employed,  depending 
upon  exposure,  pressure,  and  other  local  conditions. 

The  Sylvester  process  imparts  waterproofness  by  the  formation 
of  insoluble  compounds  due  to  chemical  action  between  the  soap 
and  alum  solutions,  the  compounds  filling  the  pores. 

Paraffine. — Cold  Process. — Applicable  to  all  classes  of  masonry 
above  ground,  whether  old  or  new;  adapted  to  protecting  against 
decay,  and  preventing  either  leakage  or  absorption  of  water.  Ma- 
terial is  paraffine  specially  treated  and  dissolved  in  volatile  carrier, 
in  saturated  solution.  A  translucent  liquid  leaving  the  surface  to 
which  it  is  applied  the  same  in  appearance  as  before.  ..  Efficient, 
easily  applied,  and  inexpensive;  covering  capacity  about  125  square 
feet  to  the  gallon  on  first  coat,  and  about  175  feet  to  gallon  on  second 
coat;  two  coats  required.  Materials  best  obtained  from  manu- 
facturers all  ready  for  use.  Has  a  high  penetrating  capacity  into 
masonry  surfaces,  and  after  application  volatile  carrier  evaporates, 
leaving  paraffine  in  the  pores. 

Precautions  to  be  employed  on  the  work: 

1.  See  that  the  material  specified  is  being  used. 

2.  Obtain  explicit  directions  from  manufacturer  and  follow  them. 

3.  Surface  to  be  treated  should  be  smooth  and  freed  from  all 
projections.     Holes  to  be  filled  up. 

4.  Surface  to  be  clean  and  thoroughly  dry,  not  only  on  surface 
but  all  the  way  in. 

5.  Material  to  be  applied  thoroughly;   well  rubbed  in,  filling  all 
corners,  recesses,  etc. 

6.  At  least  two  coats  to  be  applied. 

7.  In  severely  exposed  locations  three  coats  are  advisable. 

8.  Fire  should  be  kept  away  from  the  material  during  application. 
Paraffine. — Hot  Process. — In  this  process,  the  walls  are  first 

treated  with  artificial  heat  and  when  sufficiently  warm,  melted,  hot 

[368] 


The  Waterproofing  of  Concrete  Structures 

paraffine  wax  is  thoroughly  rubbed  in.  This  is  one  of  the  most 
durable  of  all  the  waterproofing  methods  for  work  exposed  to  the 
weather  and  for  the  preservation  of  building  stones.  It  must 
necessarily  be  applied  by  those  specially  equipped  for  and  exper- 
ienced in  the  work. 

Bituminous  Process. — Employed  for  dampproofing  exposed 
building  walls  of  superstructures  by  application  to  the  interior 
surface  of  such  walls;  for  underground  work  to  prevent  absorption 
of  ground  dampness,  and  also  for  coating  the  covered  faces  of 
building  stones  to  prevent  staining  and  discoloration  due  to  leach- 
ing of  salts  from  masonry  backing. 

Materials  must  possess  a  high  degree  of  elasticity  and  durability, 
and  when  used  on  walls,  must  have  a  gripping  power  so  that  plaster 
can  be  directly  applied  thereon. 

Materials  specially  prepared  for  these  purposes  obtained  ready 
for  use  under  various  trade  names. 

Precautions  to  be  observed  on  the  work: 

1.  See  that  the  material  specified  is  employed. 

2.  Obtain  directions  of  manufacturers  and  follow  them. 

3.  Surface  to  be  clean  and  dry. 

4.  Two  coats  to  be  applied. 

5.  First  coat  to  be  allowed  to  set  up  before  second  is  applied. 

6.  Work  to  be  well  rubbed  in  in  corners  and  recesses  and  con- 
tinuous throughout. 

7.  When  plaster  is  to  be  applied  directly  on  waterproof  film, 
wall  surface  should  be  left  rough  to  obtain  good  bond. 

8.  Work  to  be  kept  exposed  as  little  time  as  possible  after  com- 
pletion. 

9.  In  applying  plaster  upon  film  see  that  latter  is  not  in  any  way 
injured. 

Cement  Grouting  Processes. — Plain  cement  grout  has  often  been 
employed  for  a  waterproof  coating,  but  owing  to  the  fact  that  such 
coatings  will  absorb  water  by  capillarity  and  also  on  account  of  the 
difficulty  of  making  such  coatings  adhere  without  peeling,  they 
are  not  to  be  highly  recommended.  Several  excellent  prepared 
cement  grouts  are  on  the  market  which  have  been  treated  with 
water  repellants,  and,  having  high  penetrating  qualities,  they  assist 
the  bonding  to  the  masonry  surfaces.  They  are  sold  under  trade 

24  1  369  ] 


Handbook  for  Cement  and  Concrete  Users 

names  and  are  employed  to  impart  a  flat  finish  in  various  colors  to 
concrete  surfaces,  as  well  as  to  dampproof. 

Miscellaneous  Materials, — Numerous  other  materials  are  on  the 
market  for  the  purpose  of  waterproofing  superstructures.  The 
composition  is  secret  and  when  they  are  employed  the  inspector 
should  follow  the  directions  of  the  maker.  He  should,  however, 
see  that  in  any  case  at  least  two  coats  of  any  material  are  applied. 
It  is  almost  impossible  to  obtain  a  surface  free  from  pinholes  and 
other  defects,  on  the  first  application. 

Workmanship. — Whatever  method  is  employed  the  inspector 
should  always  see  that  the  surface  is  properly  prepared  and  that  the 
application  is  continuous  throughout.  Any  omissions  at  corners, 
cornices,  around  windows  and  other  points  easily  accessible  may 
prove  fatal  to  the  final  success  of  the  work. 

As  for  the  preparation  of  surfaces,  they  should  always  be  clean 
and  free  from  foreign  matter.  Where  cement  coatings  are  employed 
and  the  waterproofing  depends  upon  the  setting  of  the  cement,  the 
surfaces  should  be  damp  or  wet,  so  that  the  water  necessary  for  the 
setting  will  not  be  absorbed  by  the  masonry.  Where  the  water- 
proofing depends  upon  the  penetration  of  the  material  into  the 
pores,  the  surface  should  be  dry  to  increase  the  penetration  as  much 
as  possible. 

Surfaces  should  generally  be  smooth,  holes  filled  up  and  pro- 
jections removed.  Projections  are  likely  to  be  injured  by  scaffold- 
ing and  to  admit  water  at  such  points.  Not  only  does  a  smooth  sur- 
face make  the  application  easier  and  more  certain,  it  is  also  more 
economical  in  material. 

In  the  bituminous  process,  however,  where  the  material  is  applied 
on  the  inner  surface  of  exposed  walls  and  plaster  is  to  be  applied 
directly  on  the  waterproof  film,  the  surface  should  be  rough.  This  is 
necessary  in  order  that  the  plaster  may  properly  bond  to  the  treated 
surface.  Joints  in  brickwork  form  excellent  keys  for  such  bonding 
and  have  been  taken  advantage  of.  A  large  number  of  brick  build- 
ings have  been  treated  by  this  process. 

HOW  TO   USE    THE   TABLE 

The  accompanying  table  has  been  prepared  with  a  view  of  con- 
densing into  small  space  the  principal  features  of  modern  water- 

[370] 


The  Waterproofing  of  Concrete  Structures 


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[372] 


The  Waterproofing  of  Concrete  Structures 

proofing  processes  as  applied  to  varying  conditions,  and  to  enable 
one  having  a  waterproofing  problem  to  solve,  and  not  familiar  with 
the  subject,  to  pick  out  the  method  most  suitable  without  having  to 
read  up  the  whole  subject. 

As  previously  stated,  the  method  must  be  suited  to  the  con- 
ditions of  the  problem  if  good  results  are  to  be  had.  In  numer- 
ous cases  more  than  one  method  may  be  employed  with  good 
results  and  in  such  cases  the  methods  have  been  given  in  order  of 
their  desirability.  Local  conditions,  however,  may  make  the  order 
of  preference  different. 

Use  of  the  Table. — The  table  is  divided  into  13  columns  as  num- 
bered on  bottom. 

Columns  3  and  5  give  the  methods  of  waterproofing  for  the 
different  structures  listed  in  columns  i  and  2.  These  methods  are 
listed  by  key  letters  as  A,  B,  C,  etc.,  the  essential  features  of  which 
are  described  in  columns  7  to  13. 

Column  3  gives  the  method  of  waterproofing  that  may  be  pro- 
vided for  in  plans  and  specifications  for  new  structures  or  which 
may  be  employed  before  the  construction  work  has  advanced 
too  far. 

Column  5  gives  the  methods  available  for  the  structures  already 
erected  and  for  remedying  leaky  conditions  in  such  structures.  The 
fact  that  a  method  is  not  listed  in  column  5  means  that  it  is  not  ad- 
visable to  use  it  for  old  structures. 

As  a  practical  example  in  using  the  table,  suppose  it  is  desired 
to  dampproof  the  walls  of  a  new  brick  building  which  is  to  be 
erected  and  also  to  waterproof  the  foundation,  which  is  in  wet 
ground. 

To  Find  the  Method  from  the  Tables. — Look  up  columns  i  and  2 
for  exposed  walls;  methods  given  are  D,  B,  and  C,  in  order  of  de- 
sirability. Now  look  in  column  No.  7  and  those  following  for 
description  of  the  methods  D,  B,  and  C. 

For  the  foundation  to  resist  water  pressure  under  walls,  G,  K, 
L,  M,  are  given  in  order  of  desirability,  but  G  is  omitted  if  walls  are 
not  reinforced.  The  remarks  point  out  some  special  features  such 
as  for  L  and  M,  "  Asphalt  not  to  be  used  in  ground  polluted  by  gas 
drip,  oils,  etc.,  that  injuriously  affects  it.  This  is  an  important 
precaution." 

[373] 


Handbook  for  Cement  and  Concrete  Users 

It  is  not  claimed  that  the  arrangement  of  methods  will  in  all 
cases  be  decisive  or  that  some  methods  not  listed  may  not  be  em- 
ployed ;  but  the  use  of  the  table  will  prevent  such  glaring  but  frequent 
mistakes  as  using  a  surface  coating  for  sub-surface  work  or  using  a 
wash  on  the  inside  of  cellar  walls,  to  waterproof  against  pressure 
and  in  other  ways  prevent  the  use  of  wholly  unfit  methods. 


APPROXIMATE    COST    OF   WATERPROOFING 

The  following  table  gives  approximate  cost  of  different  classes 
of  waterproofing  which  may  be  used  as  a  basis  for  comparing  relative 
economy  of  the  methods  selected  from  the  table : 

A. — Sylvester  process,  1/2  cent  to  4  cents  per  square  foot. 

B,  D. — Dampproofing  masonry  walls,  2  coats  applied  in  place, 
2  cents  to  4  cents  per  square  foot. 

C. — Melted  paraffine,  5  cents  to  8  cents  per  square  foot. 

F. — Adds  about  10  per  cent  to  the  cost  of  untreated  mass  con- 
crete. 

G. — Cement  coatings  with  waterproofing  compounds;  i  in.  on 
floors,  1/2  in.  to  3/4  in.  on  walls,  8  cents  to  30  cents  per  square  foot, 
depending  upon  conditions. 

/. — Hot  coal  tar,  pitch,  and  felt.  Horizontal  surfaces:  first  ply, 
$2  to  $4  per  square  (100  sq.  ft.);  additional  plys,  $1.50  to  $2.50 
per  square;  vertical  surfaces  add  10  per  cent  to  25  per  cent. 

J. — Cold  process,  felt  or  burlap,  same  as  commercial  asphalt. 

K. — Pressure  work,  i  ply,  $4  to  $5  per  square. 

L. — Commercial  asphalt  and  asphalt  felt,  add  15  per  cent  to 
60  per  cent  per  ply,  depending  upon  conditions. 

L. — Special  asphalts  and  felts,  add  30  per  cent  to  50  per  cent  per 
ply. 

M. — Asphalt  mastic,  i  in.,  15  cents  per  square  foot. 


374] 


CHAPTER  XXXI 

GROUT,    OR    "LIQUID    CONCRETE,"    AND    ITS    USES 

Preparing  and  Mixing  Grout. — Mixing  Machines. — Various  Uses  of  Grout. 

Uses  of  Grout. — Grout,  or  "Liquid  Concrete,"  as  it  is  sometimes 
called,  is  a  thin,  watery  mortar,  composed  either  of  neat  cement  or 
of  cement  and  sand  mixed  in  different  proportions.  Its  principal 
uses  are  as  follows: 

1.  As  a  mortar  for  cementing  the  joints  in  masonry,  after  the 
stones  have  been  laid. 

2.  For  consolidating  loose  stones,  rocks,  or  riprap. 

3.  For  depositing  concrete  under  water. 

4.  For  waterproofing  tunnels  by  injection  behind  the  lining. 

5.  For  stopping  springs  and  leaks. 

6.  As  a  paint  for  coating  concrete  walls,  either  for  surfacing  or 
for  dampproofing. 

7.  As  a  surface  coating  in  thicknesses  of  from  3/4  to  i  inch  for 
beams,  walls,  slabs,  etc. 

8.  As  a  wearing  coat  for  sidewalks,  curbs,  cellars,  etc. 

9.  For  bonding  new  to  old  concrete. 

10.  For    levelling    up    the    bedplates    of    engines   and    other 
machinery. 

11.  As  a  filler  for  paving  blocks. 

12.  As  a  protective  coating  for  iron  and  steel. 

13.  For  surfacing  pipes  and  conduits  to  decrease  their  resistance 
to  the  flow  of  water. 

14.  For  cementing  anchor  bolts  into  their  sockets. 

Preparing  and  Mixing  Grout. — Grout  as  ordinarily  employed  is 
composed  either  of  neat  cement  or  of  cement  and  sand  in  propor- 
tions of  i  :  i  or  i  :  2.  The  best  method  of  mixing  grout  by  hand  is 
first  to  mix  the  cement  or  cement  and  sand  to  the  consistency  of 
stiff  paste  on  an  ordinary  mixing-board;  then  place  in  a  tub  or 
bucket  and  add  water  in  small  quantities  until  the  paste  is  reduced 
to  the  consistency  required.  To  facilitate  me  mixing,  the  paste 

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Handbook  for  Cement  and  Concrete  Users 

should  be  well  stirred  whije  the  water  is  being  added.  To  prevent 
the  grout  from  becoming  stiff  through  partial  set  and  thus  becoming 
sluggish  as  well  as  weak,  the  material  should  be  poured  as  soon  as 
possible  after  the  mixing.  When  poured  from  any  height,  it  is 
desirable  to  employ  neat  cement  or  rich  mixtures,  as  there  is  a 


2'grout 


2  high  pnssure  plug 


FIG.  122. — Grouting  Machine  Used  by  Board  of  Water  Supply,  New  York. 

tendency  for  the  cement  and  sand  to  separate  and  form  separate 
layers. 

The  quantity  of  water  required  for  grout  depends  upon  the 
class  of  work  in  which  it  is  employed.  Where  the  interstices 
through  which  it  is  to  be  poured  are  smaH,  it  must  be  made  thin 

[376] 


Grout,  or  "Liquid  Concrete,"  and  its  Uses 

and  watery,  otherwise  it  cannot  be  forced  beneath  the  upper  layers 
of  rock.  When  the  interstices  are  large  or  the  grout  is  applied 
under  pressure,  a  thicker  mixture  can  be  used.  It  is  always  de- 
sirable to  employ  as  thick  a  grout  as  can  be  forced  into  the  cavity 
which  it  is  intended  to  fill,  since  a  thin  grout  becomes  weak  and 
porous  after  the  water  has  evaporated. 

Where  grout  is  used  in  large  quantities,  machines  are  employed 
for  mixing,  and  the  grout  is  forced  through  pipes  under  pressure. 

Grout  Mixing  Machines. — Grout  mixing  machines  are  of  two 
general  types:  (a)  tank  mixers  and  (b)  paddle  mixers. 

In  the  tank  machine,  grout  is  mixed  by  blowing  in  air  at  the 
bottom  of  the  tank,  and  the  material  is  ejected  by  turning  the  air 
in  at  the  top  and  forcing  the  grout  through  a  hole  in  the  base.  In 
this  type,  there  are  no  stuffing-boxes  or  shafts  carrying  revolving  pad- 
dles to  wear  out  by  the  grinding  action  of  the  cement. 

The  so-called  paddle-mixing  machines  consist  in  general  of  a 
closed  steel  box  of  cylindrical  shape,  about  two  feet  in  diameter. 
Through  the  axis  of  the  cylinder  a  shaft  is  fitted.  The  shaft  makes 
about  30  revolutions  per  minute  and  carries  about  six  double 
paddles  which  thoroughly  mix  the  ingredients.  The  time  of  mixing 
occupies  about  three  minutes.  After  mixing,  air  pressure  is  ad- 
mitted to  the  cylinder  and  the  grout  is  discharged  by  means  of  a 
flexible  hose  connected  with  the  cylinder.  In  grouting  the  dry 
stone  packing  between  the  tunnel  and  rock  of  the  East  River  Tunnel 
for  the  Rapid  Transit  Subway  between  Brooklyn  and  New  York, 
a  pressure  of  90  pounds  per  square  inch  was  employed,  the  high 
pressure  being  required  to  force  the  grout  against  the  hydrostatic 
pressure  due  to  the  depth  of  the  working. 

Cementing  Joints. — Grout  is  employed  to  some  extent  for 
cementing  the  joints  in  rubble  masonry,  but  for  this  purpose  its  use 
is  not  recommended.  When  so  employed  the  interior  of  the  wall  is 
laid  up  dry.  The  grout  is  poured  on  top  of  the  wall  and  is  expected 
to  find  its  way  downward  and  fill  all  voids.  The  difficulty  with  thi:- 
method  is  twofold.  If  the  grout  is  made  thin,  it  becomes  porous 
and  weak,  and  if  made  thick,  it  fills  only  the  upper  portions  of  the 
wall.  Better  results  are  obtained  by  inserting  pipes  into  the  body 
of  the  wall  at  several  points  and  forcing  in  the  grout  under  pressure. 

Grout  was  formerly  employed  in  this  way  in  the  construction  of 

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Handbook  for  Cement  and  Concrete  Users 


bridge  piers,  where  it  was  customary  after  laying  the  large  backing 
stones  in  place  to  fill  the  vacant  spaces  with  broken  stone  of  various 
size  and  then  pour  in  as  much  grout  as  would  work  its  way  into  the 
voids.  Such  methods  are,  however,  no  longer  in  vogue  for  first- 
class  structures,  where  each  stone  is  thoroughly  bedded  in  cement 

mortar  before  the  next 
course  is  laid. 

Consolidating  Rip- 
rap.— Grout  is  legiti- 
mately employed  for  the 
purpose  of  consolidating 
loose  stone  or  riprap. 
In  order  that  the  liquid 
mortar  may  properly  fill 
the  voids  in  the  bottom 

of  the  pile,  pipes  should  be  inserted  into  the  mass 
and  the  grout  forced  in  under  pressure,  or  else  some 
special  method  adopted  for  obtaining  this  result. 

In  Engineering-Contracting,  for  May  6, 
1908,  is  given  a  description  of  the  methods  em- 
ployed by  the  U.  S.  Government  in  constructing 
locks  and  dams  on  the  upper  White  River  in 
Arkansas.  Lock  and  dam  No.  i  were  located 
about  one  mile  below  Batesville,  Ark.  The  locks 
The  were  of  concrete  masonry  while  the  dam  was  a 


Wafer  Supply' from  Force 

Pump  for  Jetting 


ment  of  Apparatus 
for  Driving. 


'rock\ 

FIG.  123. 
Clark     Steel     Pile   A.     ,  M  .  , 

Filled  with  Grout  timber  crib  structure  weighted  down  with  stone, 
Showing  Arrange-  and  provided  with  a  concrete  apron.  The  lock 
was  at  one  end  of  the  dam,  and  a  concrete 
T-shaped  abutment  was  built  at  the  other  end  to 
protect  the  shore  end  of  the  structure  from  erosion. 

The  foundation  for  this  abutment  consisted  of  a  timber  crib, 
formed  of  10  X  10  in.  squared  timbers,  with  interior  pens  varying 
in  size  from  5  X  10  ft.  to  10  X  12  ft.  These  pens  were  filled  with 
"one-man"  stones  to  weight  down  the  structure,  the  filling  averag- 
ing ii  ft.  in  depth.  The  stones  were  then  consolidated  by  filling 
the  interstices  with  Portland  cement  grout. 

The  method  of  applying  the  grout  was  as  follows : 

Before  the  filling  was  commenced,  open-ended  square  boxes, 

[378] 


Grout,  or  "Liquid  Concrete/'  and  its  Uses 

8  X  8  ins.  inside  dimensions,  were  perforated  with  i  1/2  in.  holes 
and  placed  on  end  about  10  ft.  apart.  These  were  the  distribution 
boxes  for  the  grout.  Inside  of  the  distribution  boxes,  smaller  open- 
ended  square  boxes  made  of  i-in.  boards  were  placed.  These  boxes, 
which  were  not  perforated,  measured  3X3  ins.  on  the  inside  and 
were  at  first  just  long  enough  to  reach  from  the  bottom  to  the  top 
of  the  outside  boxes.  As  the  grout  rose  in  the  rubble,  the  inside 
boxes  were  raised  and  shortened  to  compensate  for  the  depth  filled. 
By  feeding  the  grout  through  these  smaller  boxes,  which  delivered 


FIG.  124. — Arrangement  of  Pipes  for  Grouting  Rock  over  Tunnel  Roof. 

it  almost  intact  at  the  bottom  of  the  large  perforated  ones,  it  had  to 
enter  the  rubble  from  below  upward :  and  being  twice  as  heavy  as 
water,  the  filling  of  all  the  voids  was  practically  assured.  The  grout 
was  a  i  :  2  mixture  of  Portland  cement  and  sand,  and  the  cost  of 
grouting  was  at  the  rate  of  $3.65  per  cu.  yd.  of  stone  composing  the 
fill. 

Depositing  Concrete  Under  Water. — The  standard  methods  of 
depositing  concrete  under  water  are  by  means  of  a  tremie  or  trough, 
by  depositing  in  closed  buckets,  and  by  depositing  in  cloth  or  paper 
bags. 

An  older  method  which,  however,  is  not  recommended  for  first- 

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Handbook  for  Cement  and  Concrete  Users 

class  work,  is  to  deposit  loose  stone  or  riprap,  and  to  fill  the  in- 
terstices by  forcing  liquid  grout  into  the  mass  by  means  of  a  pipe 
reaching  into  the  interior. 

The  objections  to  this  method  are  the  impossibility  of  filling  the 
voids  on  account  of  the  washing  away  of  a  large  part  of  the  grout, 
and  to  the  impracticability  of  forcing  it  into  all  of  the  interstices 
between  the  stones.  For  use  in  consolidating  blocks  employed  as 
paving  for  reservoir  slopes,  the  use  of  grout  is,  however,  economical 
and  amply  sufficient  for  the  purpose. 

Grout  in  Tunnel  Linings. — One  of  the  most  useful  applications 

GROUT  PIPES 

AND  ALTERNATIVE^  ARRANGEMENT  OF  WEEPERS 


IN  UNSUPPORTED 

TUNNEL  IN  SUPPORTED  TUNNEL 

FIG.  125. — Showing  Arrangement  of  Grout  Pipes  on  Catskill  Water  Works,  New  York. 

of  grout  is  for  the  purpose  of  waterproofing  and  increasing  the 
strength  of  tunnel  linings. 

In  tunnelling  through  rock,  the  section  removed  by  blasting  is  in 
excess  of  the  requirements.  When  lined  with  iron  rings  or  concrete, 
a  space  is  left  over  the  lining  which,  if  left  unfilled,  would  permit 
the  accumulation  of  water,  causing  dampness  or  leaks  in  the  tunnel, 
and  in  the  case  of  unstable  rock,  producing  unequal  pressures,  or 
endangering  the  roof  lining  from  possible  slides.  It  is,  therefore, 
desirable  to  pack  the  space  above  the  lining  with  stone,  and  in 
submarine  tunnels  the  stone  packing  is  consolidated  and  rendered  im- 
pervious by  forcing  in  grout  to  fill  the  interstices  between  the  stones, 

[380] 


Grout,  or  "Liquid  Concrete/'  and  its  Uses 


In  the  construction  of  the  East  River  Tunnel  for  the  Rapid 
Transit  R.  R.  or  Subway  between  New  York  and  Brooklyn,  an  iron 
lining  was  employed,  and  the  space  between  the  lining  and  the  rock 
was  packed  with  stone.  In  each  segment  of  the  lining,  holes  were 
left  and  closed  by  screw  plugs.  Through  these  holes  Portland 


50  ft  or  less 
LC: 


vent  pipe  '^Weeper 


»   ~— Vent  pipe- "    (Cut-off  wall 

\jroutpipe       Grout pipe* 


FIG.  126. — Arrangement  of   Grout  Pipes  in  Tunnels  of  Catskill  Water  Works, 

New  York. 

cement  grout  was  injected  after  a  section  of  the  lining  had  been 
placed. 

The  grout  was  a  i  :  i  mixture  of  Portland  cement  and  crusher 
dust  and  was  injected  under  an  air  pressure  of  90  pounds  per  sq. 
in.  through  a  flexible  hose,  which  was  connected  with  the  i/ 4-inch 
holes  in  the  tunnel  shell. 

The  grout  was  mixed  by  means  of  a  paddle  machine.  The 
mixer  consisted  of  a  steel  cylinder,  21  in.  in  diameter  by  22  in.  long 
and  the  mixing  was  done  by  means  of  a  shaft  carrying  six  double 
paddles,  which  were  revolved  at  the  rate  of  30  revolutions  per 
minute. 


Handbook  for  Cement  and  Concrete  Users 

The  mixing  was  done  in  batches.  Each  batch  contained  three 
bags  of  Giant  Portland  cement  and  three  bags  of  crusher  dust. 
The  time  occupied  in  mixing  was  i  1/2  minutes,  and  it  required 
about  five  minutes  for  the  complete  operation  of  charging,  mixing, 
injecting  the  grout,  and  preparing  the  machine  for  the  next  batch. 

As  to  the  success  of  this  method  of  grouting,  Mr.  Robert  Ridg- 
way,  who  was  Division  Engineer  in  charge  of  the  tunnel  section, 
reported  that  the  filling  of  the  interstices  in  the  stone  packing  with 
grout  was  excellent  where  the  tunnel  was  in  rock.  Where  the  tunnel 
was  in  sand,  grout  was  forced  up  through  the  ground  and  was  found 
filling  minute  crevices  in  the  earth  all  the  way  to  the  surface. 

Stopping  Leaks  and  Seams. — Grout  has  long  been  employed  for 
filling  the  seams  in  rocks  and  for  stopping  springs  and  leaks. 

In  excavating  for  the  purpose  of  obtaining  suitable  foundations 
for  bridge  piers,  dams,  buildings  or  other  important  structures, 
and  in  sinking  shafts  and  tunnelling,  seamy  rock  and  water-bearing 
strata  are  frequently  encountered.  In  the  case  of  dams,  the  seams 
must  all  be  filled  before  the  foundation  courses  can  safely  be  started, 
since  otherwise  the  leakage  beneath  the  dam  would  tend  to  float  the 
masonry,  and  thus  endanger  the  stability  of  the  structure.  Hence 
it  is  customary  to  excavate  until  sound  rock  is  encountered,  and 
then  to  inject  grout  under  pressure  into  any  seams  or  faults  that 
may  present  themselves. 

In  the  case  of  ordinary  foundations,  the  chief  danger  from 
springs  or  flowing  water  is  the  washing  away  of  the  cement  which 
is  used  in  the  masonry.  It  is  therefore  necessary  to  take  care  of 
any  incoming  water  until  the  fresh  mortar  or  concrete  employed  in 
the  construction  has  had  time  to  set.  This  is  ordinarily  done  by 
carrying  the  water  away  in  pipes.  Where  the  pressure  is  high  the 
pipes  are  carried  up  and  the  water  permitted  to  flow  away  while 
the  lower  courses  are  being  laid.  With  a  low  pressure  or  hydrostatic 
head,  the  downward  pressure  of  the  water  in  the  pipe  may  be 
sufficient  when  carried  up  to  prevent  any  flow. 

After  the  masonry  has  been  carried  up  a  sufficient  height,  the 
stoppage  of  the  leak  is  effected  by  forcing  grout  into  the  pipe.  When 
there  is  no  flow  from  the  pipe,  the  leak  can  be  controlled  by  filling 
the  pipe  with  grout,  which  will  then  displace  the  water  and  on 
hardening  form  an  effective  plug.  Where  the  spring  flows  from  the 

[382] 


Grout,  or  "Liquid  Concrete,"  and  its  Uses 

pipe,  it  is  necessary  to  force  in  the  grout  under  pressure  and  to  main- 
tain the  pressure  until  the  cement  has  hardened,  since  otherwise 
the  flow  would  wash  away  the  grout.  .  Where  practicable,  it  is  de- 
sirable to  apply  sufficient  pressure  to  the  grout  to  cause  it  to  flow 
into  the  seams  or  porous  strata  as  well  as  to  fill  the  pipe  and  fill  the 
interstices  between  the  pipe  and  the  masonry. 

Grout  as  a  Paint. — Grout,  when  used  as  a  paint,  is  one  of  the 
surface  finishes  applied  to  mass  concrete.  When  so  employed  it 
should  be  applied  while  the  wall  is  still  green,  since  after  hardening 
the  grout  has  a  tendency  to  flake  off  in  patches.  Grout  is  also 
employed  as  a  dampproofing  paint,  but  when  so  used  it  should  be 
applied  to  the  water  side  of  the  wall,  as  it  is  far  more  effective  in 
keeping  the  moisture  from  entering  the  wall  than  it  is  in  preventing 
the  egress  of  moisture  that  has  already  entered  the  mass.  Where 
pressure  is  encountered,  however,  the  layer  of  grout  is  too  thin  to 
offer  effective  resistance  to  the  passage  of  moisture  and  under  such 
conditions,  the  wall  should  either  be  made  impervious  in  itself  or 
else  surrounded  by  a  bituminous  shield  or  mastic  of  sufficient  mass 
to  be  able  to  withstand  the  pressure. 

Surface  Finish. — Grout  is  more  effectively  employed  as  a  surface 
finish  when  it  is  applied  in  such  a  way  as  to  become  perfectly  in- 
corporated with  the  mass  of  the  wall.  This  is  ordinarily  done 
by  using  a  wet  concrete  mixture  for  filling  the  forms  and  causing  the 
grout  to  flush  to  the  surface  by  pulling  back  the  coarse  aggregate 
from  the  face  of  the  wall  with  a  spade  or  fork.  This  forms  the 
ordinary  finish  for  beams,  retaining  walls,  and  mass  constructions. 
Some  waterproof  grouts  are  now  on  the  market  which  make 
excellent  surface  finishes  for  concrete  and  which  are  made  in 
all  colors. 

Grout  for  Walks,  Etc. — Grout  or  mortar  forms  the  ordinary 
wearing  surface  for  sidewalks,  curbs,  cellar-floors,  etc.  In  such 
constructions,  the  foundation  consists  of  a  layer,  from  3  to  6  inches 
thick,  composed  of  cement,  sand,  and  i/ 2-inch  broken  stone,  while 
the  surface  coat  consists  of  cement  and  sand,  which  is  usually  3/4 
of  an  inch  thick.  To  improve  the  appearance  and  wearing  proper- 
ties of  this  coat,  granite  chips  are  also  frequently  mixed  in  with  the 
mortar  or  grout.  To  be  satisfactory  for  this  purpose,  the  chips 
must  be  hard  and  tough,  and  should  be  trowelled  in  such  a  way  as  to 

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Handbook  for  Cement  and  Concrete  Users 

bring  the  flat  portions  of  their  surfaces  uppermost,  thus  providing 
a  good  wearing  surface,  and  affording  protection  to  the  cement. 

Bonding  New  and  Old  Concrete. — Grout  is  generally  employed  in 
bonding  new  concrete  to  old.  The  surface  of  the  old  concrete  is 
first  scrubbed  with  a  steel  brush  and  a  stream  of  water,  or  a  jet  of 
steam,  or  compressed  air  to  remove  all  dirt  and  grease;  and  where  a 
good  bond  is  desired,  it  should  also  be  scratched,  etched  with  acid 
or  tooled  so  as  to  produce  indentations  that  will  serve  as  a  key. 
After  preparing  the  surface,  a  grout  composed  of  neat  cement  is 
rubbed  in  with  a  broom.  While  this  is  still  soft  it  is  covered  with  a 
layer  of  the  regular  concrete  mixture,  and  the  ordinary  work  of 
concreting  is  commenced. 

Grout  in  the  Machine  Shop. — In  setting  up  the  bedplates  of 
engines  and  stationary  machines,  lathes,  planers,  drillpresses,  and 
other  heavy  tools,  it  is  customary  first  to  block  up  the  framework  to 
the  required  height  with  wooden  blocks  and  wedges  and  then  to 
bed  the  framework  to  the  floor  or  piers  forming  the  foundation  by 
pumping  in  a  rich  mixture  of  Portland  cement  grout.  When  used 
for  this  purpose,  the  grout  should  be  mixed  as  thick  as  practicable. 
so  that  on  drying,  a  strong,  durable  mortar  will  be  formed,  which 
will  easily  support  the  weight  and  vibration  of  the  machinery  without 
crumbling  or  settling  out  of  level. 

Grout  as  a  Paving  Filler. — One  of  the  most  common  uses  for 
grout  is  as  a  filler  for  paving  blocks.  When  used  for  brick  or  stone 
pavements,  the  blocks  are  laid  dry  and  the  interstices  between  the 
stones  or  bricks  are  filled  by  pouring  in  grout  to  serve  as  a  cement. 

The  materials  commonly  employed  for  fillers  are  asphalt,  tar 
and  its  compounds,  cement,  grout,  and  sand.  The  principal  ad- 
vantages of  grout  for  this  purpose  are  as  follows:  (i)  cheapness; 
(2)  adequate  protection  to  the  edges  of  the  blocks;  (3)  prevents 
the  blocks  from  loosening;  (4)  is  watertight;  (5)  is  durable;  (6) 
permits  the  blocks  to  be  laid  close  together;  (7)  is  easy  to  keep  clean; 
and  (8)  wears  uniformly. 

The  disadvantages  of  grout  fillers  are:  (i)  its  tendency  to 
crack;  (2)  to  become  slippery;  (3)  affords  a  poor  foothold  on 
grades;  (4)  is  difficult  to  remove  without  breaking  the  blocks;  and 
(5)  causes  objectionable  noise. 

These   objections   apply   chiefly   to   brick   pavements.     Where 

[384] 


Grout,  or  "Liquid  Concrete/'  and  its  Uses 

stone  is  employed  the  irregularities  of  the  blocks  are  generally 
sufficiently  pronounced  to  prevent  them  from  becoming  slippery 
and  to  enable  the  horses  to  obtain  a  foothold  on  grades.  Stone 
blocks  are  also  less  subject  to  injury  when  removed. 

Miscellaneous  Uses. — In  addition  to  the  uses  which  have  thus 
far  been  briefly  enumerated  in  this  chapter,  grout  is  employed  as  a 
protective  coating  for  iron  and  steel,  for  surfacing  pipes  and  conduits 
to  decrease  their  resistance  to  the  flow  of  water  and  for  many  other 
purposes.  The  distinction  between  mortar  and  grout  is  but  one  of 
degree.  While  the  excess  of  water  contained  in  grout  tends  to 
increase  its  porosity  over  that  of  cement  mortar,  yet  for  many  pur- 
poses its  use  is  not  only  legitimate  but  unexcelled. 

Grout  is  not  a  safe  substitute  for  mortar  in  laying  up  masonry 
or  in  important  constructions  under  water.  It  can,  however,  be 
forced  into  cracks  and  crevices  which  thick  mortar  is  unable  to 
penetrate,  and  thus  for  stopping  springs  and  leaks,  rilling  voids 
between  the  lining  and  roof  of  tunnels,  filling  the  crevices  in  founda- 
tions for  dams  and  other  structures,  and  for  numerous  other  pur- 
poses, grout  is  extensively  employed  in  engineering  works;  while 
its  minor  uses  such  as  surfacing,  painting  iron,  steel  and  concrete, 
filling  between  paving  blocks,  dampproofing,  and  levelling  of  founda- 
tion areas  have  extended  the  employment  of  this  material  to  many 
kinds  of  construction,  although  other  considerations  both  theoretical 
and  practical  have  tended  to  circumscribe  its  use. 


CHAPTER  XXXII 

INSPECTION  OF  CONCRETE  WORK— A  SUMMARY  OF 
ESSENTIAL  RULES  AND  PRINCIPLES  OF  CON- 
STRUCTION, FOR  SECURING  GOOD  CONCRETE 
WORK 

The  Work  of  the  Inspector. — Inspection  of  the  Cement,  Sand,  and  Aggregates. — Pro- 
portioning and  Mixing. — Inspection  of  Forms,  Reinforcement  and  Placing  Con- 
crete.— Rules  for  Removing  Forms. — Rules  for  Surface  Finish. — Rules  for 
Blocks,  Piles,  and  Castings. 

CAREFUL  inspection  is  essential  in  all  concrete  work.  The  best 
design  will  come  to  naught  unless  it  be  carried  out  with  the  aid  of 
careful  and  skilful  workmanship  and  the  use  of  good  materials. 
Good  construction  can  be  assured  only  when  the  work  is  under  the 
control  of  competent  and  conscientious  inspectors. 

The  Work  of  the  Inspector. — The  work  of  the  inspector  may  be 
divided  into  the  following  parts: 

1.  Inspection  of  the  cement,  sand,  and  aggregate;    a.  quality; 
b.  storage. 

2.  Proportioning,  measuring,  and  mixing  of  the  ingredients. 

3.  Inspection  of  forms,  arch-centres,  column  moulds,  etc. 

4.  Placing  of  the  reinforcement. 

5.  Placing  of  the  concrete. 

(a)  General  rules. 

(b)  In  reinforced  work. 

(c)  In  hot  weather. 

(d)  In  freezing  weather. 

6.  Bonding  new  to  old  work. 

7.  Removal  of  the  forms. 

8.  Surface  finish. 

9.  Moulded  blocks,  piles,  ornamental  castings,  etc. 
Inspection  of  the  Cement. — Cements  are  subjected  to  laboiatory 

tests  to  determine  their : 

(a)  Fineness. 

(b)  Time  of  set. 

386 


Inspection  of  Concrete  Work 

(c)  Soundness. 

(d)  Specific  gravity. 

(e)  Strength. 

•(a)  Fineness  is  determined  by  passing  the  cement  through 
sieves  of  various  meshes  and  noting  the  percentages  retained. 

(b)  Time  of  set  is  found  by  making  pats  of  the  cement  and 
noting  the  time  required  to  resist  the  penetration  of  wires  of  specified 
weight. 

(c)  Soundness  is  tested  by  noting  the  condition  of  the  edges  of 
the  pats;    also  by  subjecting  pats  to  a  steam  bath  and  observing 
whether  they  blow,  swell,  or  crack. 

(d)  Specific  gravity  is  determined  by  weighing  a  given  volume 
in  air  and  noting  the  loss  of  weight  when  immersed  in  a  liquid  of 
known  specific  gravity,  such  as  alcohol,  which  does  not  act  on  the 
cement. 

(e)  Strength  is  determined  by  moulding  briquettes  of  i  sq.  in. 
sectional  area,  permitting  them  to  remain  in  air  and  under  water 
for  specified  periods,  and  then  breaking  in  testing  machines,  and 
noting  the  breaking  loads. 

Cement  should  be  stored  in  its  original  package,  until  ready 
for  use.  It  should  also  be  kept  in  a  clean,  dry  place.  If  stored  in 
a  damp  place,  the  cement  will  partially  set  and  become  valueless  for 
construction  purposes. 

Inspection  of  Sand  and  Aggregates. — Sand  for  impervious  con- 
crete should  be  silicious  in  character,  of  graduated  size,  and  with 
coarse,  rounded  grains.  Sand  should  also  be  clean,  but  excessive 
cleanliness  is  not  essential  as  an  admixture  of  clay  in  amounts  up 
to  10  per  cent  results  in  no  material  reduction  in  the  strength  of 
mortars.  A  small  percentage  of  clay  also  tends  to  increase  the 
imperviousness  of  the  concrete. 

When  specifications  call  for  sharp  sand,  the  grains  should  be 
angular.  Sharp  sand  was  until  quite  recently  always  required  by 
engineers,  on  account  of  its  binding  properties.  Recent  experiments, 
however,  indicate  that  sand  with  rounded  grains  is  less  liable  to 
fracture;  and  when  graduated,  so  that  the. smaller  grains  fit  between 
the  larger  ones  without  wedging  them  apart,  is  far  more  impervious 
when  used  in  mortar  or  concrete. 

The  best  aggregates  for  concrete  are  trap  rock  and  gravel. 

[387] 


Handbook  for  Cement  and  Concrete  Users 

Hard  limestones  and  granite  are  also  good.  Soft  limestones,  sand- 
stones and  schists  are  less  durable,  while  slate,  shale,  and  cinders 
are  poor  materials  to  use.  The  size  of  the  aggregate  is  of  importance. 
In  massive  work,  the  stone  should  pass  through  a  2  1/2  inch  ring, 
in  reinforced  concrete  beams,  the  diameter  should  not  exceed  3/4 
of  an  inch. 

Rules  for  Proportioning,  Measuring,  and  Mixing. — American 
engineers  proportion  concrete  mixtures  by  measure,  thus:  a  1:2:3 
concrete  is  one  composed  of  i  volume  of  cement,  3  volumes  of  sand, 
and  6  volumes  of  aggregate. 

The  duty  of  the  inspector  is  to  make  certain  that  the  specified 
proportions  are  accurately  and  uniformly  adhered  to.  This  requires : 

(a)  That  definite  measuring  units  be  employed. 

(b)  That  the  accuracy  of  the  measure  boxes,  hoppers,  etc.,  be 
verified. 

(c)  That  the  filling  of  the  measuring  boxes,  hoppers,  etc.,  be 
exact. 

(d)  That  when  two  or  more  boxes  or  hoppers,  filled  with  sand 
or  stone,  go  to  make  up  a  batch,  the  exact  number  be  employed  for 
each  and  every  batch. 

Cement  differs  in  volume  when  measured  loose,  and  when 
packed  in  the  barrel;  cement  barrels  also  vary  in  capacity.  Hence 
the  engineer,  contractor,  and  inspector  should  reach  an  agreement  as 
to: 

(a)  Whether  the  cement  is  to  be  measured  loose  or  packed. 

(b)  What  the  cubic  contents  of  a  barrel  or  bag  of  cement  shall  be 
called. 

The  measures  used  should  be  tested  to  make  sure  that  each  holds 
the  amount  intended.  This  can  be  very  simply  done  by  using  a 
known  measure  to  fill  the  measuring  box  employed,  or  the  volume 
of  the  box  can  be  mathematically  computed. 

When  automatic  measuring  devices  are  used  to  proportion  the 
cement,  the  inspector  should  see: 

(a)  That  they  are  regulated  to  give  the  proper  proportions. 

(b)  That  the  materials  do  not  clog,  choke,  or  arch  in  the  feed 
hoppers. 

(c)  That  the  feed  hoppers  are  kept  amply  supplied  with  mate- 
rials. 

[388] 


Inspection  of  Concrete  Work 

Concrete  is  mixed  by:  i.  Hand  turning  with  shovels  and  hoes; 
2.  Machine  mixing. 

Rules  for  Hand  Mixing. — Rule  i.  The  batches  should  be  of  such 
size  that  they  can  be  proportioned  without  using  fractions  of  mea- 
sures. 

Rule  2.  Mix  the  cement  and  sand  dry  with  hoes  or  shovels. 

Rule  3.  Over  the  dry  sand  and  cement  mixture  spread  the 
broken  stone  which  has  been  previously  wetted  and  on  top  of  the 
stone  apply  water  evenly. 

Rule  4.  Finally  turn  the  whole  the  specified  number  of  times  with . 
shovels. 

Rule  5.  The  quantity  of  concrete  in  each  batch  should  be  not 
greater  than  can  be  mixed  and  deposited  before  the  cement  begins  to 
set. 

Rules  for  Machine  Mixing. — Concrete  mixers  are  of  three  types: 

(a)  Batch  mixers. 

(b)  Continuous  mixers. 

(c)  Gravity  mixers. 

In  batch  mixers  the  materials  are  charged,  mixed,  and  discharged 
in  batch  units;  in  continuous  mixers  the  materials  are  discharged  in 
a  continuous  stream;  and  in  gravity  mixers  the  materials  are  caused 
to  mingle  by  falling  through  specially  constructed  troughs,  tubes,  or 
hoppers. 

Rule  i.  The  mixer  should  be  of  an  approved  type,  and  operated 
in  such  a  manner  as  to  mix  the  materials  uniformly  and  efficiently. 

Rule  2.  If  a  batch  mixer  is  used,  the  batch  should  be  (a)  com- 
posed of  the  proper  proportions,  (b)  thoroughly  mixed,  and  (c) 
completely  dumped  out  as  a  unit. 

Rule  3.  When  a  continuous  mixer  is  used,  the  materials 
must  be  (a)  fed  evenly  into  the  mixer  in  the  proper  proportions; 
(b)  the  automatic  measuring  devices  must  work  accurately,  and  (c) 
the  material  must  not  "bridge"  or  " choke,"  and  so  cease  to  feed 
into  the  mixer  drum. 

Rule  4.  The  mixer  must  be  given  the  requisite  number  of  turns 
for  each  batch,  as  determined  by  trial. 

Rule  5.  The  concrete  in  discharging  from  the  mixer  should  not 
drop  any  considerable  distance. 

Rule  6.  The  mixer  should  be  cleaned  of  all  adhering  mortar  or 

[389] 


Handbook  for  Cement  and  Concrete  Users 

concrete  when  work  is  discontinued,  as  such  cakes  are  liable  to 
break  or  jar  loose  and  be  discharged  as  an  inert  body  into  the  next 
batch. 

Inspection  of  Forms. — Forms  are  the  moulds  in  which  concrete 
is  shaped,  and  it  is  the  duty  of  the  inspector  to  see  that  they  are  of 
ample  strength,  efficiently  braced  and  in  proper  alignment.  The 
following  rules  should  also  be  observed : 

Rule  i.  The  lumber  should  be  of  such  quality,  size,  and  finish  as 
to  promise  absolute  stability  and  reasonably  perfect  work  under  the 
conditions. 

Rule  2.  Forms  should  be  oiled  or  wetted  just  before  the  concrete 
is  deposited  to  prevent  sticking.  Oil  should  be  used  where  a  smooth 
surface  is  desired.  It  should  not  be  used  where  the  concrete  is  to 
be  plastered  or  whitewashed,  as  the  grease  will  discolor  the  work 
and  weaken  the  bond. 

Rule  3.  White  pine,  yellow  pine,  spruce,  Oregon  pine,  and  red- 
wood are  suitable  for  forms;  hemlock  is  unreliable. 

Rule  4.  Forms  should  be  thoroughly  cleaned  of  shavings,  chips, 
sawdust,  dirt,  or  other  accumulations  just  before  the  concrete  is 
placed. 

Rule  5.  The  construction  of  the  forms  should  be  such  that  they 
can  be  removed  without  injury  to  the  concrete. 

Rule  6.  All  forms  must  be  erected  in  exact  alignment,  both 
vertically  and  horizontally;  column  and  wall  forms  should  be  plumb; 
girder  boxes  and  wall  forms  without  winds  or  twists;  arch  and  slab 
centres  level :  the  alignment  must  be  watched  during  the  placing  of 
the  concrete,  as  the  loading  may  distort  the  forms. 

Rule  7.  Forms  should  be  (a)  of  ample  strength;  (b)  of  sufficient 
rigidity  not  to  deflect  unduly  under  load,  and  (c)  horizontal  forms 
should  be  given  a  camber  to  prevent  them  from  deflecting  below  the 
horizontal.  A  common  camber  is  1/2  inch  for  every  10  feet  of  span. 

Rule  8.  The  carpenter  work  should  be  accurate,  the  lines  true 
and  square,  the  joints  close  and  the  finish  neat.  All  forms  must  be 
planed  where  required  to  produce  a  smooth  surface  finish. 

Rule  9.  All  joints  in  forms  should  be  tight  enough  to  prevent 
leakage  of  the  grout  from  the  liquid  mass. 

Rule  10.  Column  moulds  must  be  accurately  spaced  in  all 
directions  and  set  square  with  the  lines  laid  down  on  the  plans. 

[390] 


Inspection  of  Concrete  Work 

Rule  ii.  Column  moulds  should  be  cleaned  with  scrupulous 
care,  as  they  are  liable  to  get  the  sweepings  from  girder  boxes  and 
other  debris.  To  facilitate  cleaning  the  bottom  of  the  mould  should 
be  left  open  on  one  side  until  just  before  pouring  the  concrete. 

Rule  12.  The  wire  ties  for  wall  forms  must  be  in  place  and 
drawn  taut  so  as  to  pull  the  sides  close  against  the  spacers.  The 
spacers  must  be  removed  from  the  forms  as  soon  as  they  are  reached 
by  the  concreting. 

Rule  13.  Bolts  which  can  be  withdrawn  should  be  used  instead 
of  wire  as  ties  for  forms  where  the  surface  is  left  exposed,  as  a  rust 
spot  invariably  forms  on  the  face  of  the  wall  where  a  wire  is  cut. 

Rule  14.  Where  bolts  are  used  as  ties,  the  bolts  must  be  with- 
drawn and  the  holes  filled  with  mortar  after  the  forms  have  been 
removed.  To  facilitate  withdrawing,  the  bolts  must  be  greased. 

Rule  15.  Forms  for  retaining  walls  with  battered  sides,  py- 
ramidal forms  for  column  footings,  etc.,  should  be  firmly  anchored 
down  to  resist  the  up-thrust  or  floating  effect  of  the  semi-liquid 
concrete. 

Rule  1 6.  Arch  centres  must  be  framed,  assembled,  and  erected 
in  a  workmanlike  manner.  Substantial  foundations  are  required; 
also  suitable  means  for  striking  or  lowering  the  centre  gradually  and 
without  shock  or  jar  to  the  concrete.  Allowance  should  also  be 
made  for  settlement  under  load  and  for  permanent  camber.  The 
lagging  should  be  of  even  thickness  and  planed  smooth  in  order  to 
give  a  good  surface  to  the  soffit  of  the  arch. 

Placing  of  the  Reinforcement. — Concrete  is  weak  in  tension  but 
strong  in  compression.  Reinforcement  is  placed  on  the  tension 
sides  of  beams  to  make  up  for  the  weakness  of  the  concrete.  The 
number,  size,  and  spacing  of  the  bars  must  be  in  exact  conformity 
with  the  engineer's  plans,  otherwise  the  structure  may  be  materially 
weakened.  The  position  of  the  bars  in  the  form  is  of  no  less  im- 
portance than  their  proper  number  and  size,  as  they  are  designed 
to  be  in  the  position  where  they  will  most  add  to  the  strength 
of  the  construction. 

The  following  rules  should  also  be  observed : 

Rule  i.  Where  the  steel  is  received,  it  should  be  checked,  assort- 
ed, and  stored  in  such  a  way  as  to  be  reasonably  protected  from  rust, 
dirt,  oil,  and  paint. 


Handbook  for  Cement  and  Concrete  Users 

Rule  2.  In  the  assembling  of  the  reinforcement,  the  exact 
number,  size,  form,  spacing,  and  location  of  bars,  stirrups,  ties, 
spacers,  etc.,  called  for  by  the  plans  must  be  strictly  adhered  to. 

Rule  3.  The  steel  should  be  free  from  paint,  scale,  dirt,  and  ex- 
cessive rust.  Concrete  which  has  lodged  on  the  steel  and  hardened 
during  previous  work  must  also  be  removed  before  the  reinforcement 
is  finally  concreted  in. 

Rule  4.  Bars  should  be  bent  in  such  a  manner  that  they  do  not 
break  or  crack  at  the  bend.  The  bending  force  should  be  applied 
gradually  and  not  with  a  jerk.  Cold  bending  is  always  preferable; 
if  hot  bending  is  allowed,  it  must  be  done  in  such  a  way  that  the  bar 
is  not  burned  or  weakened. 

Rule  5.  Splicing  of  bars,  lapping,  wiring,  use  of  sleeves  and  set 
screws,  etc.,  must  be  carried  out  as  directed  by  the  engineer. 

Rule  6.  Protruding  ends  of  bars  which  are  left  for  splicing  should 
be  coated  with  cement  paint  to  diminish  rusting,  and  guarded 
against  being  bent  or  loosened. 

Rule  7.  All  reinforcement  must  be  securely  fastened  to  preserve 
spacing,  location,  alignment,  etc. 

Rule  8.  The  wiring  of  reinforcement  at  intersections  should  be 
done  carefully  and  strongly,  using  No.  16  or  No.  18  B.  and  S.  gauge 
soft  black  wire. 

Rule  9.  In  column  reinforcement,  the  reinforcing  frame  should 
be  concentric  with  that  of  the  column  below,  the  bars  vertical,  all 
ties  in  place  and  taut,  and  all  splices  made  according  to  specifications. 
No  part  of  the  steel  should  touch  the  walls  of  the  form  and  the  space 
between  the  steel  and  form  should  be  uniform. 

Rule  10.  Templets  should  be  used  especially  at  bottom  and  top 
of  column  to  insure  accurate  spacing  of  bars. 

Rule  ii.  Column  bars  should  be  spliced  as  follows: 

In  a  butt  joint  the  ends  should  be  square,  the  bearing  uniform, 
and  the  joint  be  held  true  to  line  by  sleeves  or  splice  bars. 

If  lap  joints  are  allowed,  the  wire  wrappings,  cable  splices,  etc., 
must  be  made  taut  and  secure. 

Rule  12.  Beam  reinforcement  should  be  placed  symmetrically 
with  the  axis  of  the  beam,  the  bottom  bars  kept  at  the  required 
height  above  the  bottom  of  the  beam,  the  proper  space  maintained 
between  the  reinforcement  and  the  sides  of  the  beam,  and  the  re- 


Inspection  of  Concrete  Work 

quired  connections  made  at  the  ends  of  the  beam  with  the  column 
bars  or  the  reinforcement  of  abutting  beams  or  walls.  All  planes 
and  lines  should  be  true  and  all  parts  of  the  reinforcement  wired 
together  or  otherwise  held  firmly  in  position. 

Placing  of  the  Concrete. — Before  the  practice  of  reinforcing  con- 
crete came  into  general  use,  specifications  called  for  dry  mixtures, 
thorough  tamping,  and  depositing  in  uniform  horizontal  layers.  In 
reinforced  work,  dry  mixtures  do  not  flow  readily  around  the  bars, 
while  tamping  is  liable  to  throw  them  out  of  position.  Hence  in 
such  work  wet  mixtures  are  used  and  puddling  or  slicing  takes  the 
place  of  tamping.  This  consists  in  churning  and  cutting  the  wet 
mixtures  with  rods  or  slice  bars  to  work  out  air  bubbles,  close  up 
pockets,  and  settle  the  materials. 

The  following  rules  should  also  be  observed : 

Rule  i.  Buckets  should  just  clear  the  work  when  discharged, 
as  when  the  materials  are  allowed  to  drop,  they  are  liable  to  jar  the 
forms  and  displace  the  reinforcement  and  at  the  same  time  produce 
separation  of  the  stone  from  the  mortar. 

Rule  2.  In  depositing  through  chutes,  care  must  be  taken  to 
detect  any  separation  of  the  stone  from  the  mortar. 

Rule  3.  Pouring  should  be  done  at  several  points  over  the  area 
to  be  filled  so  as  to  reduce  flowing  and  spreading  to  a  minimum. 

Rule  4.  The  concrete  must  be  poured  before  it  has  begun 
to  set. 

Rule  5.  Dry  mixtures,  when  specified,  should  be  deposited  in 
even  layers  not  exceeding  6  to  8  ins.  in  thickness  and  thoroughly 
tamped  with  rams  heavy  enough  to  thoroughly  compact  the  concrete 
and  bring  a  film  of  water  to  the  surface. 

Rule  6.  Wet  mixtures  should  be  well  puddled,  so  as  to  work  out 
air  bubbles  and  pockets  and  bring  the  concrete  into  close  contact 
with  the  reinforcement  at  every  point. 

Rule  7.  In  making  slabs,  the  full  thickness  should  be  poured  in 
one  continuous  operation.  If  possible  slab  and  beam  should  be 
made  monolithic. 

Rule  8.  Beams  should  be  poured  in  one  continuous  operation 
from  bottom  to  top,  the  concrete  worked  closely  around  the  rein- 
forcement by  puddling,  and  the  stone  worked  back  from  the  sides  by 
spading. 

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Handbook  for  Cement  and  Concrete  Users 

Rule  9.  When  beam  and  slab  are  designed  to  act  together  as  a 
T-beam,  both  must  be  poured  in  one  operation. 

Rule  10.  Columns  must  be  poured  well  ahead  of  the  beams. 
The  operation  should  be  continuous  from  the  base  to  the  underside 
of  supported  beam  or  girder,  and  the  concrete  well  puddled  by  bars 
long  enough  to  go  easily  between  the  outside  of  the  reinforcement 
and  the  inside  of  the  form. 

Rule  ii.  In  concreting  arches,  the  arch  ring  should  be  divided 
into  sections  of  such  size  that  the  pouring  of  each  can  be  made  a 
continuous  operation.  In  longitudinal  sections,  the  concrete  should 
be  begun  simultaneously  at  both  skewbacks  and  continued  uniformly 
and  continuously  to  the  crown.  Where  the  sections  are  transverse 
or  across  the  arch,  the  better  practice  is  to  concrete  the  crown  section 
first  and  work  towards  both  skewbacks  a  pair  of  sections,  one  on 
each  side,  at  a  time. 

Rule  12.  In  depositing  under  water,  the  concrete  should  be  kept 
as  free  as  possible  from  wash  which  will  float  off  the  fine  cement 
from  the  mixture.  The  concrete  should  never  be  allowed  to  drop 
through  any  considerable  depth  of  water.  The  standard  methods 
of  depositing  under  water  are  in  bags,  in  closed  buckets',  and  through 
tremies. 

Rule  13.  In  hot  weather,  great  care  must  be  exercised  to  prevent 
the  concrete  from  drying  out  before  it  has  set.  The  aggregate 
should  be  thoroughly  wetted,  more  water  used  in  the  mixing, 
and  if  necessary,  the  work  should  be  covered  with  planks  or 
tarpaulins. 

Rule  14.  In  freezing  weather  concreting  should  be  stopped  at 
the  temperature  required  by  the  specifications.  When  salt  is  added 
to  prevent  freezing,  the  amount  should  not  exceed  10  per  cent  of 
the  weight  of  the  water.  Other  methods  of  protection  are  heating 
the  materials,  housing  in  the  work,  covering  with  tarpaulins,  using 
artificial  heaters,  and  adding  calcium  chloride  in  amounts  equal  to 
about  2  per  cent  of  the  volume  of  the  mortar. 

Bonding  New  to  Old  Work. — The  surface  of  concrete  which  has 
hardened  has  a  skin  or  coating  to  which  fresh  concrete  will  not 
adhere.  This  skin  must  be  removed  and  the  surface  prepared 
for  the  new  material.  The  methods  employed  are,  to 

(a)  Prepare  the  surface  by  scrubbing,  washing,  and  grouting. 

[394] 


Inspection  of  Concrete  Work 

(b)  Etch  the  surface  with  an  acid  wash,  and  thoroughly  remove 
the  acid  by  washing. 

(c)  Break  the   surface  with  steam,   air  blast  or  water  under 
pressure. 

In  stopping  work  over  night,  the  following  rules  should  also  be 
observed : 

Rule  i.  In  slabs,  the  concrete  should  be  stopped  in  a  vertical 
plane  at  right  angles  to  the  span  either  (a)  at  midspan,  or  (b)  over 
the  centre  of  the  supporting  beam  or  girder. 

Rule  2.  In  beams  or  girders,  the  concrete  should  be  stopped  in 
a  vertical  place  at  right  angles  to  the  length  of  the  beam  either 
(a)  at  midspan,  or  (b)  over  the  centre  of  the  supporting  column. 

Rule  3.  Columns  should  be  stopped  at  the  level  of  the  bottom 
of  the  beam  or  girder  which  they  support. 

Rule  4.  Walls  should  be  stopped  in  vertical  planes  across  the 
wall;  if  practicable  the  stoppage  should  occur  where  an  expansion 
joint  is  to  come. 

Removal  of  the  Forms. — All  forms  must  be  taken  down  without 
straining  or  jarring  the  freshly  placed  concrete.  The  greatest  care 
must  be  exercised  to  prevent  workmen,  who  are  taking  down  forms, 
from  dropping  a  single  piece  of  lumber  on  the  floor. 

Shores  for  floors  or  arches  must  never  be  removed  in  less  than 
two  weeks  after  the  concrete  is  placed.  In  damp  or  cold  weather, 
they  should  remain  in  place  at  least  four  weeks.  Centres  for  long- 
span  arches  should  remain  in  place  from  one  to  three  months. 
Before  removing  shores  on  extra  long  spans,  it  is  advisable  to  put 
horizontal  saw  cuts  completely  through  the  shores.  If  weakness 
then  develops,  it  will  simply  close  up  the  saw  cuts  and  the  shores 
will  continue  to  do  their  duty. 

Rule  i.  Moulds  for  ornamental  or  indented  castings  must  be 
so  constructed  that  they  can  be  removed  piece  by  piece  without 
injury  to  the  concrete. 

Rule  2.  Forms  should  not  be  removed  until  the  concrete  has 
hardened  sufficiently  to  carry  its  load.  Forms  should  remain 
longer  under  beams  and  arches  than  around  columns  and  walls,  and 
longer  under  arches  of  long  than  of  short  span.  Forms  should  not 
be  removed  until  the  concrete  is  hard  enough  to  ring  clearly  when 
struck  with  a  hammer. 

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Handbook  for  Cement  and  Concrete  Users 

Rule  3.  Under  average  conditions,  forms  should  remain  in  place 
for  the  following  periods : 

Walls  in  mass  work  from  i  to  3  days. 

Thin  walls  and  columns  from  2  to  5  days,  according  to  weather 
conditions  as  noted  above. 

Slabs  up  to  6  feet  span,  from  i  to  2  weeks. 

Beams  and  girders,  from  2  to  4  weeks. 

Small  arches,  from  i  to  3  weeks;  large  arches  from  i  to  2  months. 

Rule  4.  Forms  should  be  removed  gently  without  chipping  "or 
jarring  the  concrete.  Prying  with  bars  or  striking  with  a  sledge 
should  be  prohibited. 

Rule  5.  Column  forms  should  be  so  constructed  as  to  permit  of 
their  removal  without  disturbing  the  beam  or  slab  forms. 

Rule  6.  Beam  forms  should  be  so  constructed  as  to  permit  of 
the  removal  of  the  sides  before  the  bottom  is  disturbed  in  order  that 
the  condition  of  the  concrete  can  be  examined. 

Rule  7..  Beams  should  be  supported  by  shores  for  a  considerable 
time  after  the  forms  have  been  removed,  or  until  the  concrete  has 
become  thoroughly  cured. 

Rule  8.  Arch  centres  must  be  removed  without  shock  or  jar  to 
the  arch  ring.  Centres  should  be  lowered  evenly  and  gradually, 
so  that  the  ring  can  settle  uniformly. 

Rules  for  Surface  Finish. — Surface  finishes  are  of  two  kinds: 

(a)  Those  in  which  the  moulded  surface  is  treated  after  the 
forms  are  removed. 

(b)  Those  in  which  the  moulding  is  so  done  that  the  finish  is  a 
part  of  the  moulding  process. 

The  following  rules  should  be  observed  for  class  (a) : 

Rule  i.  If  the  surface  is  to  be  grouted  all  holes  and  joint  marks 
must  be  filled  or  smoothed  down  before  the  grout  is  applied. 

Rule  2.  When  the  surface  is  to  be  tooled,  from  30  to  60  days 
must  elapse  before  the  concrete  is  hard  enough  to  give  a  good,  clean 
tool  cut. 

Rule  3.  When  scrubbed,  the  scrubbing  should  be  continued  just 
long  enough  to  remove  the  surface  cement  and  to  partially  expose 
the  aggregate  without  loosening  it. 

Rule  4.  When  etched  with  acid,  the  acid  must  not  be  allowed 
to  remain  too  long,  and  all  excess  acid  must  be  removed  by  washing. 

[396] 


Inspection  of  Concrete  Work 

Spaded  or  mortar  finishes  are  used  for  class  (b).  The  following 
rules  should  be  observed : 

Rule  i.  Spading  is  best  done  with  a  special  flat-bladed  spade, 
having  the  blade  perforated  with  holes  or  slots,  which  will  screen 
back  the  stones  and  allow  the  mortar  to  pass. 

Rule  2.  In  a  mortar  finish,  the  facing  mortar  and  concrete  back- 
ing are  placed  at  the  same  time  and  are  tamped  together.  The 
tamping  should  not  be  so  hard  as  to  force  pieces  of  stone  through 
the  facing,  but  hard  enough  to  bond  thoroughly  the  facing  mortar 
and  backing. 

Rule  3.  The  preferable  method  of  construction  is  to  use  a  facing 
form  between  the  lagging  and  the  backing.  Fill  between  the  facing 
form  and  the  lagging  with  mortar,  then  fill  behind  the  facing  form 
with  the  backing,  and  finally  withdraw  the  facing  form  and  tamp 
backing  and  facing  together. 

Moulded  Blocks,  Piles,  Ornamental  Castings,  Etc. — Three  general 
processes  are  employed  for  moulding  cast  concrete  work : 

(a)  A  dry  mixture  is  heavily  tamped  into  a  mould  and  the  block 
is  immediately  released  and  set  aside  for  curing. 

(b)  A  liquid  mixture  is  poured  into  moulds  where  the  blocks 
remain  until  hard. 

(c)  A    medium   wet    mixture    is   compressed    into    moulds   by 
hydraulic  presses  or  other  means  of  securing  great  pressure. 

The  following  rules  should  be  observed  for  Dry  Mixture  Blocks. — 

Rule  i.  For  dry  mixtures  the  mixing  and  tamping  must  be 
thorough  and  the  water  uniformly  distributed.  Tamping  should 
begin  with  the  first  shovelful  and  should  be  continued  until  the 
mould  is  filled. 

Rule  2.  Dry  mixtures  should  have  a  consistency  such  that  the 
block  will  part  from  the  mould  without  sticking,  sloughing,  sagging, 
or  loss  of  form.  Dryness  in  excess  of  these  requirements  should  not 
be  allowed. 

Rule  3.  Moulds  must  be  rigid  and  adequately  clamped.  The 
construction  should  be  such  that  the  green  blocks  are  not  injured 
when  removed. 

Rule  4.  After  removal,  the  dry  mixture  blocks  must  be  stacked 
in  a  horizontal  position  on  immovable  supports  and  freely  sprinkled 
with  water.  A  dry  mixture  block  does  not  have  enough  mixing 

[397] 


Handbook  for  Cement  and  Concrete  Users 

water  to  enable  the  cement  to  set  and  harden  perfectly,  and  this 
deficiency  must  be  supplied  by  sprinkling.  The  sprinkling  should 
begin  within  an  hour  after  moulding  and  should  continue  for  at 
least  ten  days.  While  the  block  is  soft,  the  sprinkling  should  consist 
of  a  gentle  spray,  that  will  not  wash  the  concrete. 

Rule  5.  Blocks  should  be  cured  for  at  least  30  days  before  they 
are  removed  from  the  storage  yards  for  use  in  construction. 

The  following  rules  apply  to  wet  mixtures:  Rule  i.  The  mixture 
must  be  thoroughly  stirred  and  churned  to  eliminate  air  voids, 
prevent  arching  and  fill  corners  and  edges  of  moulds. 

Rule  2.  The  mould  must  not  be  removed  until  the  concrete  has 
thoroughly  set  and  is  hard  enough  to  do  without  its  support. 

Rule  3.  The  block  must  be  true  to  shape  and  exact  in  dimensions, 
with  faces  true  to  plane,  and  edges  true  to  line.  Mouldings  and 
other  ornamentations  must  be  perfect.  A  moulded  block  should 
be  equal  in  perfection  to  cut  stone  in  all  particulars  of  shape  and 
dimensions. 

Rules  for  Concrete  Piles. — Concrete  piles  are  driven  (a)  by 
punching  a  hole  in  the  ground  by  means  of  a  metal  mould  and 
filling  with  concrete ;  (b)  by  casting  the  piles  in  moulds  and  driving 
by  aid  of  a  water  jet. 

The  following  rules  should  be  observed  for  concrete  piles  in 
place : 

Rule  i.  In  driving  the  shell  for  new  piles,  care  must  be  taken 
that  adjacent  piles  in  which  the  concrete  is  still  green  are  not  jarred 
and  injured. 

Rule  2.  In  concreting  piles  in  place,  the  concrete  must  be 
lowered  in  small  buckets  or  in  such  a  way  that  the  cement  is  not 
separated  from  the  stone. 

Rule  3.  The  reinforcement  must  be  set  parallel  to  and  concentric 
with  the  axis  of  the  pile.  The  best  practice  is  to  assemble  the  rein- 
forcement into  a  unit  frame,  and  to  place  it  as  a  unit. 

The  following  should  be  observed  for  cast  piles: 

i.  Cast  piles  should  be  straight,  the  metal  points,  when  used, 
firmly  attached  and  the  pile  should  be  without  cracks  or  chipping. 
None  of  the  reinforcing  metal  should  be  exposed.  If  cored  for 
sinking  by  water  jet,  the  cores  must  be  open  and  unobstructed. 
If  fluted  on  the  sides  to  provide  passages  for  the  rise  of 

[398] 


Inspection  of  Concrete  Work 

water    used    in  jetting,   the  flutes  or    corrugations    must  not  be 
obstructed. 

2.  Moulds  should  be  straight  and  kept  true  to  line  and  level. 

3.  The  reinforcement  must  be  kept  parallel  to  and  concentric 
with  the  axis  of  the  mould. 

4.  The  concrete  should  be  poured  at  several  points  along  the 
mould  to  prevent  flowing  and  segregation. 

5.  The  driving  should  be  done  in  such  a  way  that  the  pile  is  not 
fractured  in  the  body.     The  head  should  be  protected  by  a  cushion 
cap  to  take  the  direct  blow  of  the  hammer.     If  the  driving  is  done 
by  a  water  jet,  the  pile  should  settle  to  a  firm  bearing. 

6.  Cast  piles  should  not  be  dragged  along  the  ground  or  other- 
wise roughly  handled. 

Ornamental  Castings. — In  ornamental  castings,  great  care  must 
be  taken  in  the  moulding,  handling,  and  setting  in  place  to  preserve 
the  true  lines,  flutings,  and  other  ornamentations.  When  white 
cements,  stainless  mortars,  or  other  special  materials  are  required, 
the  inspector  should  take  particular  pains  to  insure  the  use  of  the 
proper  ingredients.  The  general  rules  for  cast  blocks  and  piles 
apply  with  additional  force  to  all  ornamental  work. 


[399] 


CHAPTER  XXXIII 

COST  OF  CONCRETE  WORK 

General  Cost  of  Main  Classes  of  Work. — Elements  of  Cost. — Cost  of  Materials. — 
Cost  of  Mixing. — Cost  of  Placing. — General  Expenses. — Summary  of  Costs. — Cost 
of  Mortar. — Actual  Examples  of  Cost. — Building  Blocks. — Paving. — Removing 
Efflorescence. — Stucco. — Forms. — Cost  of  Buildings  in  Terms  of  Cubical  Con- 
tents.— Cost  of  Residences. — Cost  of  Sewers. — Concrete  Pipes. — Bridge  Piers  and 
Bridges. — Piles. — Trestles,  Sidewalks,  Curbs,  and  Gutters. — Fence  Posts. — Poles. 
— Roofs. — Tunnel  Lining. — Waterproofing. — Cost  of  Concrete  Dams. 

THE  cost  of  concrete  construction  is  made  up  of  the  combined 
cost  of  materials  and  labor.  The  cost  of  materials  for  any  given 
class  of  work  is  readily  determined  from  the  dimensions  of  the 
structure  and  the  market  prices  of  cement,  sand,  broken  stone, 
timber,  steel,  etc.;  the  labor  cost,  however,  is  dependent  not  only 
upon  the  prevailing  rate  of  wages,  but  also  upon  the  efficiency  of 
the  men  employed,  the  amount  of  form  work,  and  the  character  of 
the  construction. 

The  cheapest  construction  is  obtained  when  the  concrete  is 
deposited  in  large  masses  and  when  the  transportation,  mixing,  and 
depositing  in  place  is  performed  by  machinery.  When  laid  in  thin 
sections,  as  in  tunnel  linings,  small  arches,  thin  walls,  etc.,  the  use 
of  forms  and  of  hand  labor  per  cubic  yard  of  concrete  is  very  largely 
increased,  which  greatly  augments  the  unit  cost  of  the  construction. 

General  Cost  of  Main  Classes  of  Work. — Where  Portland  cement 
can  be  obtained  at  $1.50  per  barrel,  sand  at  80  cents  per  cubic  yard, 
and  broken  stone  at  $1.50  per  cubic  yard  delivered  on  the  work; 
and  where  the  cost  of  form  timber  does  not  exceed  $25.00  per  M; 
while  the  rate  of  wages  for  carpenters  is  $3.50,  laborers,  $1.75,  and 
teams  $3.75  per  ten-hour  day,  the  cost  of  concreting,  including 
interest  and  depreciation  on  plant,  but  with  no  allowance  for  profits, 
will  run  about  as  follows: 

Heavy  mass  constructions,  as  large  dams,  reservoir  -v 

walls,  pavements,  heavy  foundations,  abutments,  rubble  [•  $3.50  to   $5.oo  per  cu.  yd. 
concrete,  etc. 

[400] 


Cost  of  Concrete  Work 

Foundation  footings  and  difficult  mass  construction.       6.00  to     8.00  per  cu.  yd. 
Thin  rough  walls,  sewers,  and  culverts 8.00  to  10.00  per  cu.  yd. 

Thin  tooled  or  reinforced  walls  and  heavy  buildings  "1 

and  bridges,  difficult  pneumatic  and  submarine  construc- 

...  ,  .  ,  ,  .   ,        ,  r  10.00  to  15.00  per  cu.  yd. 

tions  which  are  subject  to  delays,  remforced-concrete  re- 

taining  walls,  etc. 

Light  reinforced-concrete  buildings  having  thin  walls,  \ 

slabs,  and    columns,  light    reinforced-concrete  bridges,  >  15.00  to  20.00  per  cu.  yd. 
arches,  etc. 

Elements  of  Cost. — The  various  elements  which  enter  into  the 
cost  of  plain  and  reinforced  concrete  may  be  summarized  as  follows : 

1.  Cost  of  cement,  aggregate,  and  reinforcement  at  the  work. 

2.  Cost  of  loading  the  materials  into  barrows,  buckets,  or  cars, 
and  of  their  transportation  to  the  mixer  and  dumping. 

3.  Cost  of  mixing:    (a)  Hand-mixing;    (b)  Machine-mixing. 

4.  Cost  of  loading  the  concrete  into  barrows,  buckets,  or  cars, 
and  of  its  transportation  to  the  work. 

5.  Cost  of  bending,  placing,  and  wiring  the  reinforcement  into 
position. 

6.  Cost  of  dumping,  spreading,  slicing,  spading,  and  ramming. 

7.  Cost  of  forms:   (a)  Timber,  nails,  wire,  and  other  materials; 
(b)  Carpenter's  labor. 

8.  Cost  of  plant,  storage  house,  runways,  etc. 

9.  Cost  of  engineering,  inspection,  time-keeping,  and  general 
expenses. 

10.  Interest  on  the  investment,  repairs,  depreciation  of  plant,  etc. 

11.  Profits. 

Cost  of  Cement. — The  cost  of  cement  depends  upon  the  class, 
brand,  quantity,  kind  of  package,  freight-rates  by  rail  or  water,  and 
cartage. 

At  New  York,  the  prices  in  large  lots  delivered  alongside  of 
the  docks  are  at  the  time  of  publication  as  follows  for  large  lots: 

Natural  cement    *o.8o  per  barrel 

Portland i-43      " 

Imported  2-42 

At  the  mill  Portland  cement  can  be  obtained  in  bulk  at  $1.00  per 
barrel. 

On  many  of  the  irrigation  projects  in  the  West,  where  the  haul 

26  [  4oi  ] 


Handbook  for  Cement  and  Concrete  Users 

from  the  nearest  railroad  is  considerable,  the  cost  of  cement  varies 
from  $2.50  to  $3.00  per  barrel  delivered;  at  a  dam  recently  com- 
pleted at  Hume,  Cal.,  the  cement  cost  a  little  over  $5.00  per  barrel,* 
the  high  cost  being  due  to  the  location  of  the  work,  which  necessitated 
a  great  deal  of  hauling  and  handling. 

Cement  when  ordered  in  wooden  barrels  costs  10  cents  more  per 
barrel  than  in  bulk  ;  when  ordered  in  cloth  sacks,  a  charge  of  10 
cents  per  sack  is  made,  but  on  return  of  the  sacks,  a  credit  of  8  to 
10  cents  per  sack  is  allowed;  when  ordered  in  paper  bags  the  cost 
is  5  cents  more  per  barrel  than  in  bulk. 

Hence  a  barrel  of  cement,  costing  $1.40  in  bulk  and  containing 
four  bags  to  the  barrel,  will  command  the  following  prices,  depend- 
ing upon  the  package  in  which  it  is  sent : 

1.  In  wooden  barrels $i  .40  +  .  10  =  $i  .50 

2.  In  cloth  sacks i  .40  4-  .40  =     i  .80 

3.  In  paper  sacks i .  40  +  .  05  =     i .  45 

4.  In  cloth  sacks,  which  are  returned $i  .40  to  $1.48. 

Cost  of  Sand. — The  cost  of  sand  varies  from  20  cents  to  $1.00 
per  cu.  yd.,  depending  upon  the  need  of  washing  and  the  length  of 
haul.  Standard  grades  of  Long  Island  washed  sand  are  quoted  at 
35  cents  alongside  the  docks  at  New  York;  white  quartz  sand  at 
60  cents;  and  white  quartz  grit  at  75  cents  per  cu.  yd.  for  full  cargo 
lots  of  500  cu.  yd. 

Cost  of  Gravel. — The  cost  of  gravel  varies  from  50  cents  to  $1.50 
per  cu.  yd.  Washed  gravel  alongside  of  dock  at  New  York  sells  at 
75  cents  in  cargo  lots  and  white  quartz  roofing  gravel  at  $1.30  per 
net  ton. 

Cost  of  Broken  Stone. — The  cost  of  broken  stone  varies  from 
60  cents  to  $1.50  per  cu.  yd.  Alongside  of  the  dock  at  New  York 
the  prices  are  90  cents  to  $1.00  for  i-i/2-in.  stone;  $1.00  to  $1.10 
for  3/4-in.  stone,  and  90  to  95  cents  for  screenings.  The  contract 
for  furnishing  the  Department  of  Docks,  City  of  New  York,  with 
15,000  cu.  yds.  of  stone  was  awarded  recently  at  $1.04  to  $1.06  per 
cu.  yd.,  including  the  services  of  men  to  load  the  buckets  and  empty 
them  on  the  dock,  the  city  furnishing  the  power. 

Cost  of  Steel  for  Reinforcement. — At  the  mill  plain  bars  3/4 

*  Engineering  Record,  Jan.  15,  1910. 
t  432  ] 


Cost  of  Concrete  Work 


inch  and  larger  vary  in  price  from  $1.25  to$i.8o  per  cwt.,  and  smaller 
bars  from  $1.50  to  $2.30  per  cwt.  Twisted  bars  are  held  at  an  ad- 
vance of  from  10  to  25  cents  per  cwt.  over  plain  bars,  while  the  prices 
of  other  deformed  bars  vary  according  to  the  shape,  but  are  in  gen- 
eral higher  than  those  of  twisted  bars.  Expanded  metal  varies  in 
price  from  2.80  to  8.30  cents  per  sq.  ft.  at  New  York,  according 
to  the  mesh  and  weight;  triangular  mesh,  from  .67  to  2.55  cents  per 
sq.  ft.  in  carload  lots;  expanded  lath  from  n  1/2  to  14  cents  per  sq. 
yd.,  at  mill  for  black,  and  from  18  1/2  to  21  cents  per  sq.  yd.  for 
galvanized,  and  diamond  lath  from  14  to  20  cents  per  sq.  yd.  at  New 
York  for  black. 

Total  Cost  of  Materials. — This  varies  according  to  the  proportions 
of  cement,  sand,  and  stone  or  gravel,  and  the  price  of  each  ingredient. 
With  cement  at  $1.50  per  bbl.,  sand  at  80  cents,  and  broken  stone 
at  $1.20  per  cu.  yd.,  the  quantity  of  materials  and  their  cost  for 
different  mixtures  would  be  as  follows: 

PLAIN  CONCRETE,  COST  OF  MATERIALS  per  cubic  yards,  with 

Cement  at  $i .  50  per  barrel. 
Sand       "       .  80  per  cubic  yard. 
Stone       "     1.20     "      "         " 


1:2:4  Mixture. 

i  : 

2^:5  Mixture. 

i: 

3  :  5  Mixture. 

Cement  1.46  bbl.  at  $1.50  .  .  . 
Sand    .41  cu.  yd.  at     80 

$2.19 
.33 

i.  20  at 

.4.2  at 

$1.50  $1.80 
$.   80    .                .34. 

1.13  at 
.4.8  at 

Si.  50  

.80 

$1.70 

•7Q 

Stone  .82  cu.  yd.  at  1.20.  .  .  . 
Cost  of  materials  per  cu.  yd 

.98 

$•?.  CQ 

.84  at 
Cost. 

1.  2O  I.OI 

.80  at 
Cost 

1.  2O  

. 

.96 

Cost  of  Loading  into  Barrows,  Buckets,  Etc. — Under  average 
conditions,  one  man  should  be  able  to  load  17.5  cu.  yds.  of  aggregate 
into  a  barrow  in  10  hours.  With  wages  at  $1.75  per  day,  the  cost 
per  cu.  yd.  of  materials  handled  would  be  10  cents.  For  the  1:21/2:5 
mixture  the  cost  of  loading  per  cu.  yd.  of  concrete  would  be : 

Sand      .42  cu.  yd.  at  ro  cents 4.20 

Stone      .84  cu.  yd.  at  10  cents  8.40 

Cement  .17  cu.  yd.  at  10  cents    1.70 

Total  for  i  cubic  yard 14-30 

[403] 


Handbook  for  Cement  and  Concrete  Users 

Cost  of  Transportation  and  Dumping. — This  depends  upon  the 
grade  and  length  of  haul  and  will  vary  from  5  to  10  cents  per  cu. 
yd.  of  concrete.  Mr.  H.  P.  Gillette,  in  his  "Handbook  of  Cost 
Data,"  gives  the  following  rules  for  the  cost  of  transportation  of 
materials  to  the  mixing  board : 

1.  With  barrows:  "To  a  fixed  cost  of  4  cents  (for  lost  time),  add 
i  cent  for  every  20  ft.  of  distance  from  stock  pile  to  mixing  board  if 
there  is  a  steep  rise  in  the  runway,  but  if  the  runway  is  level  add  i 
cent  for  every  30  ft.  distance  of  haul." 

2.  With  a  horse  and  cart:   "To  a  fixed  cost  of  5  cents  (for  lost 
time  at  both  ends  of  haul),  add  i  cent  for  every  100  ft.  of  distance 
from  stock  pile  to  mixing  board." 

Cost  of  Hand  Mixing. — This  will  vary  from  25  to  40  cents  per 
cu.  yd.,  according  to  the  efficiency  of  the  labor  and  the  number  of 
times  the  materials  are  turned  over  with  shovels.  With  wages  at 
17.5  cents  per  hour,  and  men  turning  over  mortar  and  concrete  at 
the  rate  of  3  cu.  yds.  per  hour,  the  cost  per  cu.  yd.  would  be  5.8 
cents  for  each  turn.  The  cement  and  sand  for  each  cu.  yd.  of 
concrete  will  measure  about  .45  cu.  yds.  If  6  turns  are  given  to 
this  mixture,  the  cost  of  turning  the  mortar  will  be  .45  X  6  X  5.8 
cts.  =  15.7  cents.  If  the  stone  and  mortar  are  turned  3  times, 
the  cost  of  mixture  will  be  3  X  5.8  =  17.4  cents.  Hence  the 
total  cost  of  turning  is  15.7  +  17.4  =  33.1  cents  per  cu.  yd.  of 
concrete. 

Cost  of  Machine  Mixing. — The  labor  cost  of  mixing  will  vary 
from  2  to  8  cents  per  cu.  yd.,  and  the  cost  and  maintenance  of  the 
mixer  from  6  to  15  cents,  according  to  the  size  and  kind  of  mixer 
and  the  percentage  of  time  which  the  machinery  is  idle. 

If  a  3/4  yd.  batch  mixer  is  employed,  200  cu.  yds.  are  readily 
mixed  in  one  day  with  three  men  to  attend  to  the  machinery.  The 
cost  of  oil,  fuel,  and  labor  per  day  will  total  about  $7.00;  or  3.5 
cents  per  cu.  yd.  of  concrete. 

In  the  Engineering  Record  of  May  21,  1910,  is  given  the  actual 
maintenance  cost  of  four  mixers  owned  by  the  Aberthaw  Construc- 
tion Co.,  of  Boston,  who  run  a  ledger  account  for  each  mixer. 
In  this  article,  it  is  shown  that  the  highest  maintenance  cost  was 
13.95  cents  per  cu.  yd.,  the  lowest  5.4  cents,  and  the  average  of  the 
four  mixers  8.94  cents. 

I  404  ] 


Cost  of  Concrete  Work 

Taking  an  average  cost  of  maintenance  at  9  cents,  and  the  cost 
of  mixing  at  3.5  cents,  the  combined  cost  or  the  cost  of  machine 
mixing  will  total  9  +  3.5  =  12.5  cents  per  cu.  yd.  for  a  batch  mixer 
of  average  size  in  steady  use. 

Cost  of  Loading  and  Transporting  to  Place. — When  loaded  by 
hand  into  barrows,  the  cost  is  less  than  that  of  loading  the  raw 
materials,  since  the  volume  of  the  concrete  is  less  than  that  of  the 
unmixed  ingredients  and  should  average  about  12  cents  per  cu.  yd. 
When  mixed  by  machinery,  the  concrete  is  dumped  directly  into 
barrows  or  cars  without  cost  of  handling. 

The  cost  of  transportation  by  barrows  or  carts  will  be  about  the 
same  as  that  for  hauling  the  raw  material,  or  from  5  to  10  cents  per 
cu.  yd.  When  conveyed  by  means  of  a  hoist  or  cableway,  the  ex- 
penses for  power,  labor,  and  maintenance  will  total  from  3  to  8 
cents  per  cu.  yd. 

Cost  of  Dumping,  Spreading,  Ramming,  Slicing,  Spading,  Etc. — 
These  will  vary  with  the  character  of  the  work  and  the  consistency 
of  the  mixture.  In  mass  work  with  a  wet  mixture  the  cost  will 
average  15  cents  per  cu.  yd.  If  a  dry  mixture  is  used,  the  expense 
of  tamping  may  increase  this  amount  to  30  or  40  cents.  In  building 
construction  the  cost  of  slicing  to  cause  the  material  to  flow  around 
the  reinforcing  bars  and  of  spading  to  pull  back  the  coarse  aggregate 
from  the  surface  will  total  from  25  to  35  cents  per  cu.  yd. 

Cost  of  Forms. — White  pine,  yellow  pine,  spruce,  and  Oregon 
pine  are  used  for  surface  forms.  Hemlock,  although  unsatisfactory, 
is  used  in  rough  constructions. 

Prices  of  timber  in  sizes  and  grades  suitable  for  form  construction 
are  as  follows  at  New  York  at  the  time  of  publication. 

Spruce  boards,  i  in.  thick  in  car  lots   $25.00  per  M  ft.  B.  M. 

Spruce  studding,  2  in.  thick  in  car  lots  ....     25.00  to  $30.00  per  M  ft.  B.  M. 

Hemlock  boards  i  in.  thick    18.00  per  M  ft.  B.  M. 

Hemlock  studdings,  2  in.  thick     20.00  per  M  ft.  B.  M. 

North  Carolina  Pine,  2  in.  thick,     20.00  per  M  ft.  B.  M. 

Long  Leaf  Yellow  Pine,  dimension  sizes    .  .     30.00  to  $40.00  per  M  ft.  B.  M. 

The  labor  cost  of  framing,  erecting,  and  removing  forms  will  run 
from  $5.00  to  $20.00  per  1,000  ft.  B.  M.,  and  the  cost  of  form  work 
per  cu.  yd.  of  concrete  in  place  will  depend  upon : 

(i)  The  size  of  the  walls,  slabs,  arches,  etc.,  since  a  thin  wall 

[405]' 


Handbook  for  Cement  and  Concrete  Users 

requires  more  form  work  per  cu.  yd.  of  concrete  in  place  than  one  of 
massive  construction.  ± 

(2)  The  number  of  times  each  form  can  be  used  in  the  course  of 
the  construction. 

(3)  The  salvage  value  of  the  material  after  the  work  is  completed. 
In  ordinary  walls,  arches,  piers,  etc.,   which  can  be  erected 

without  elaborate  false  work,  the  cost  of  form  work  will  run  from 
20  cents  to  $1.00  per  cu.  yd.  of  concrete  in  place.  In  reinforced- 
concrete  buildings,  forms  will  cost  in  place  from  5  to  20  cents  per 
sq.  ft.  of  surface  in  contact  with  concrete,  or  in  general  from  $2.50 
to  $10.00  per  cu.  yd.  of  concrete  in  place. 

Cost  of  Reinforcement  in  Place. — In  ordinary  beams,  slabs, 
columns,  retaining  walls,  etc.,  from  0.70  to  1.25  per  cent  of  rein- 
forcement is  used.  Where  i  per  cent  of  steel  is  employed,  the 
volume  of  steel  per  cu.  yd.  of  concrete  will  be  0.27  cu.  ft.,  and  the 
weight  .27  X  490  =  132  pounds. 

The  cost  of  handling,  bending,  and  assembling  steel  reinforcing 
bars  will  run  from  $5.00  to  $15.00  per  ton,  or  from  1/4  to  3/4  cents 
per  pound.  Where  plain  bars  are  used  at  a  cost  of  i  1/2  cents  per 
lb.,  at  the  mill,  the  cost  of  freight  and  wagon  haul  to  the  work  1/4 
cent  per  lb.,  and  the  cost  of  handling  and  wiring  in  place,  1/2  ct. 
per  lb.,  the  total  cost  of  i  per  cent  of  reinforcement  in  place  would  be 
i  1/2  +  1/4  +  1/2  =  2  1/4  cents  per  lb.,  or  2  1/4  X  132  =  $2.97 
per  cu.  yd.  of  concrete. 

General  Expenses. — These  include:  (a)  cost  of  plant,  storage 
buildings,  runways,  etc.;  (b)  engineering,  inspection,  time-keeping, 
and  (c)  interest  on  the  investment,  repairs,  depreciation  of  plant,  etc. 

In  a  well-equipped  organization  the  general  expenses,  after 
deducting  the  salvage  value  of  the  plant  should  not  exceed  15  per 
cent  of  the  cost  of  materials  and  labor. 

When  work  is  done  by  contract,  and  the  preliminary  surveys, 
plans,  and  specifications  are  so  complete  and  fair  as  to  reduce  the 
chances  of  loss  to  a  minimum,  a  reasonable  profit  to  the  contractor 
would  be  15  per  cent  of  the  cost  in  addition  to  the  interest  on  his 
investment.  When,  however,  there  is  much  uncertainty  as  to  the 
probable  cost  for  materials  or  labor,  or  where  the  specifications  are 
unduly  severe,  the  contractor  will  be  likely  to  raise  his  bid  to  an 
amount  20  or  even  30  per  cent  above  the  estimated  cost  of  the  work. 

[406] 


Cost  of  Concrete  Work 

Summary  of  Cost. — The  cost  of  mixing  and  placing  concrete 
where  no  expense  for  forms  is  incurred,  as  in  a  street-paving  job, 
may  be  estimated  as  follows : 


Cost  of  loading  cement  and  aggregate  

Hand 
Mixing. 

id. 

Machine 
Mixing. 

Wheeling  60  ft.  in  barrows  (4+3  cts.)  .... 

O7 

Mixing  

•u/ 

Loading  concrete  into  barrows  

•66 
12 

Wheeling  60  ft.  in  barrows  (4+3  cts.)  

O7 

0*7 

Spreading  and  ramming  

T  C 

.u/ 

T  £ 

•  XJ 

•  Lb 

General  expenses,  15  per  cent  

$0.88 
1  3 

$0.67 

Total  cost  of  labor $i  .01  $o .  77 

Cost  of  materials  for  a  f  Cement  at  81.50  per  bbl.       \ 

i   :2  1/2:5    mixture  <  Sand        "      .80  percu.  yd.  >      $3.15  ^S-^-S 

with  '  Stone       "     1.20  per  cu.  yd.  ) 


Net  cost  per  cu.  yd $4.16  $3.92 

When  the  work  is  done  by  contract,  add  from  15  to  30  per  cent  for  profit. 

(  For  mass  work  from  $0.20  to  $1.00. 
Where  forms  are  required,  add  per  cu.  \  _        .     .... 

,  .  i  For    building    construction,    from    $2.50 

yd.  concrete  in  place.  / 

I      to  $10.00. 

Where  reinforcement  is  used,  add  for  (  ^ 

.          .  \  For  mass  work,  $2.00  to  $4.00. 

each  i  percent    of  steel  per  cu.  •{  _     ,.,,. 

/  For  building  construction,  $2.25  to  $4.25. 
yd.  of  concrete  in  place. 

In  building  construction,  tunnel-lining,  thin  walls,  arches,  etc., 
where  much  spading  and  slicing  is  required;  also  where  very  dry 
mixtures  are  used,  necessitating  much  ramming,  the  cost  of  spread- 
ing and  ramming  will  be  increased  to  from  $.20  to  .50  per  cu.  yd. 

In  difficult,  pneumatic,  submarine,  and  other  work  subject  to 
delays  in  transporting  and  placing,  the  cost  of  mixing  and  placing 
concrete  will  be  increased  from  25  to  100  per  cent. 

In  general,  heavy  mass  work  will  cost  from  $4.00  to  $7.00; 
heavy  arches  from  $7.00  to  $10.00,  heavy  building  construction  from 
$10.00  to  $15.00  and  light  reinforced  buildings  from  $15.00  to 
$20.00  per  cu.  yd.  for  concrete  in  place. 

Cost  of  Mortar. — This  depends  upon  the  proportions  of  cement 
and  sand  and  the  cost  of  each  ingredient.  With  sand  containing 
45  per  cent  of  voids,  and  a  barrel  of  cement  holding  3.8  cu.  ft.  the 

[407] 


Handbook  for  Cement  and  Concrete  Users 

quantities  of  each  per  cu.  yd.  of  mortar  would  be  as  follows,  accord- 
ing to  Gillette:* 


Proportions  of  Cement  to  Sand. 

i  to  i 

i  to  ij 

I  tO  2 

I  tO  2^ 

i  to  3 

i  to  4 

No.  of  bbls.  of  Portland  cement  
No  of  cu  yds  of  sand 

4-32 
o  60 

3-6i 
o  80 

3-10 
O  QO 

2.72 
I    OO 

2.16 

I  OO 

1.62 
i  .00 

With  cement  at  $1.50  per  bbl.,  and  sand  at  $0.80  per  cu.  yd.,  the 
cost  of  i  cu.  yd.  of  i  to  2  mortar  would  be  as  follows: 

For  materials — 

3.10  X  81.50  =  $4.65 
.90  X    0.80  =      .72 


*5-37 
Labor,  transportation,  and  mixing    i.oo 


Total  cost $6.37 

To  the  above  must  be  added  the  cost  of  placing,  whether  for 
plastering,  grouting,  laying  up  masonry,  etc. 

SOME    ACTUAL    EXAMPLES    OF   COST  OF  CONCRETE 

WORK 

In  the  remaining  pages  of  this  chapter,  the  actual  costs  of  placing 
concrete  in  recently  erected  structures  of  different  types  are  pre- 
sented. In  each  instance  the  authority  is  stated  and  a  brief  descrip- 
tion is  given,  including,  wherever  possible,  a  summary  of  the  elements 
entering  into  the  cost. 

Cost  of  Grouting. — In  Engineering-Contracting  for  May  6, 
1908,  the  cost  of  grouting  a  rock-fill  dam  recently  constructed  on  the 
Upper  White  River,  in  Arkansas,  is  given  at  $3.65  per  cu.  yd.  of 
loose  rock  in  place. 

Cost  of  Concrete  Building  Blocks. — In  a  paper  read  before  the 
Iowa  Cement  Users'  Association  in  1905,  Mr.  L.  L.  Bingham  states 
that  the  average  cost  of  materials  and  labor  for  mixing,  moulding, 
and  curing  concrete  blocks  in  Iowa  with  average  wages  at  $1.83 
per  day,  is  10  1/3  cts.  per  sq.  ft.  of  face  of  wall  for  lo-inch  walls. 
This  is  made  up  of  2  cts.  for  sand,  41/2  cts.  for  cement  at  $1.60  per 


*  Gillette's  "  Hand  Book  of  Cost  Data.' 


Cost  of  Concrete  Work 

bbl.,  and  34/5  cts.  for  labor.  General  expenses,  including  interest, 
depreciation  of  plant,  and  profits  combine  to  double  this  amount,  so 
that  the  selling  price  is  about  21  cts.  per  sq.  ft.  of  wall. 

Cost  of  Concrete  Paving  Blocks. — In  a  paper  read  before  the 
National  Association  of  Cement  Users,  in  1910,  Mr.  Geo.  C.  Wright  * 
gives  the  following  data  as  to  the  cost  of  2 -inch  cubes  made  of 
Portland  cement,  sand,  and  i/  2-inch  gravel,  as  used  for  a  roadway 
pavement  by  the  New  York  State  Highway  Commission  on  1,600 
ft.  of  experimental  roadway  near  Rochester,  N.  Y. 

uThe  cost  per  square  yard  of  the  cubes  laid  was  as  follows: 
Cement,  0.088  bbl.,  $0.1 21 ;  cost  of  factory,  $0.107;  labor  of  manu- 
facture, $0.161;  gravel  at  50  cts.  per  cu.  yd.,  $0.024;  carting, 
$0.027;  laymg>  $0.072;  total  cost  per  sq.  yd.  laid,  $0.512. 
There  were  placed  on  shoulders  219  cu.  yds.  of  gravel  covering 
i, 800  sq.  yds.,  and  costing  $2.12  per  cu.  yd.  rolled  in  place,  or 
26  cts.  per  sq.  yd." 

Cost  of  Surfacing. — According  to  Ransome,  Gillette,  and  Neher, 
a  concrete  face  can  be  bush-hammered  by  an  ordinary  laborer  at 
a  cost  of  from  i  1/2  to  2  1/2  cts.  per  sq.  ft.,  wages  of  common 
laborers  being  1 5  cts.  per  hour. 

In  Engineering-Contracting,  Dec.  9,  1908,  Mr.  Linn  White, 
Engineer  South  Park  Commission,  states  that  the  cost  of  etching 
3,466  ft.  of  2 5 -ft.  cement  walk  in  Chicago  was  at  the  rate  of  i  2/3 
cts.  per  sq.  ft.  This  produced  an  excellent  finish. 

Cost  of  Removing  Efflorescence  with  Acid. —Mr.  H.  P.  Gillette  f 
states  that  the  cost  of  removing  efflorescence  on  a  concrete  bridge  at 
Washington,  D.  C.,  by  scrubbing  with  a  solution  of  i  part  hydro- 
chloric acid  and  5  parts  of  water  was  at  the  rate  of  20  cts.  per  sq. 
yd.  for  plain  walls,  and  60  cts.  per  sq.  yd.  for  the  entire  bridge,  in- 
cluding the  balustrades. 

Cost  of  Tooling  Surface. — In  Engineering  News,  Jan.  14, 1909,  Mr. 
L.  C.  Wason  gives  the  actual  cost  of  tooling  the  concrete  surface  of  a 
mill  at  Attleboro,  Mass.,  as  at  the  rate  of  5.6  cts.  per  sq.  ft.  of  area. 

In  a  paper  presented  to  the  National  Association  of  Cement 
Users,  at  their  annual  convention  in  1907,  Mr.  Henry  H.  Quimby, 
M.Am.S.C.E.,  states  that  the  cost  of  tooling  concrete  surfaces  by 


*  Engineering  Record,  March  5,  1910,  p.  277.  f  "  Hand  Book  of  Cost  Data." 

[409] 


Handbook  for  Cement  and   Concrete  Users 

means  of  a  bush  hammer  or  axe,  operated  by  hand  or  pneumatic 
power,  without  subsequent  cleaning  with  acid,  was  found  to  be 
from  3  to  12  cents  per  sq.  ft.,  according  to  the  character  and  extent 
of  the  work  and  the  equipment.  Mr.  Quimby  also  states  that  the 
cost  of  scrubbing  with  wire  brushes  is  trifling  if  done  at  the  right 
time.  A  laborer  may  wash,  say,  100  sq.  ft.  in  an  hour  if  the  material 
is  green,  or  the  same  area,  if  it  has  been  permitted  to  get  hard,  may 
take  two  men  a  whole  day  to  rub  into  shape. 

Cost  of  Applying  Stucco. — The  cost  of  applying  Portland  cement 
stucco  to  frame  houses  by  the  use  of  expanded  metal,  or  similar 
fabric  nailed  to  the  studding  strips,  will  run  from  $1.10  to  $1.40  per 
sq.  yd. 

Cost  of  Reinforced-Concrete  Building  Construction. — Mr. 
Leonard  C.  Wason,*  M.Am.Soc.C.E.,  in  a  valuable  paper  presented 
to  the  Fifth  Annual  Convention  of  the  National  Association  of 
Cement  Users  in  1909,  gave  the  following  actual  costs  of  forms  and 
concrete  in  place  as  compiled  by  the  Aberthaw  Construction  Co., 
Boston,  Mass.,  from  their  office  records:  f  [See  Table  on  page  412.] 

Cost  per  Ton. 

Cost   of  bending,  fabricating,  and  placing    (     Highest $16.47 

of  steel   in  dollars  per  ton,    omitting  •<     Lowest 2  54 

the  first  cost  of  the  material.  (     Average  of  21 ...      8.52 

Deductions  from  Table. — The  following  deductions  from  Mr. 
Wason's  figures  by  the  authors,  while  not  scientifically  exact,  are 
nevertheless  sufficiently  accurate  to  roughly  approximate  the 
average  cost  of  constructing  reinforced-concrete  buildings  in  terms 
of  the  number  of  cubic  yards  of  concrete  employed. 

Averaging  the  mean  costs  for  each  class  of  construction,  gives 
the  following  unit  costs: 

Forms  $.111  per  sq.  ft.  of  area,  or  assuming  that  each  sq.  ft.  of  area  cor- 
responds to  1/54  of  a  cubic  yard  of  concrete,  the  cost  would  be  per  cu.  yd.  of 

concrete  in  place,  $.  1 1 1  X  54,  or $6 .  oo 

Concrete  per  cu.  yd.,  $3.04  X  27,  or 8.21 

If  i  per  cent  of  steel  is  used,  the  weight  of  steel  per  cu.  yd.  of  concrete  in 
place  will  be  132  pounds.  At  a  cost  of  i  K  cts.  per  Ib.  delivered  at  the  work, 
the  cost  of  the  reinforcement  per  cu.  yd.  of  concrete  would  be  $.175  X  132,  or  2  .31 

16.52 

*  President    Aberthaw   Construction  Co.,    Boston,  Mass.       f  Engineering  News, 
Jan.  14,  1909,  page  43. 


Cost  of  Concrete  Work 

Brought  forward  from  previous  page $16.52 

At  a  mean  cost  of  $8.52  per  ton,  the  cost  of  placing  this  reinforcement  would 
be  $.00426  per  lb.,  or  $.00426  X  132  per  cu.  yd.  of  concrete,  or 0.56 

Average  cost  of  concrete  work  in  buildings  containing  i  per  cent  of  steel 
per  cu.  yd.  of  concrete  in  place $17 .08 

Cost  of  Buildings  in  Terms  of  their  Cubical  Contents. — At  the 

annual  meeting  of  the  Association  of  Cement  Users  in  1907,  Mr. 
Emile  G.  Perrot,  in  a  paper  on  "Comparative  Cost  of  Reinforced 
Concrete  Buildings,"  gave  the  following  costs  for  concrete  buildings 
built  by  his  firm  in  terms  of  their  cubical  contents : 

Warehouses  and  factories 8-1 1  cts.  per  cu.  ft. 

Stores  and  loft  buildings 11-17  cts-  Per  cu-  ft- 

Miscellaneous,  such  as  schools  and  hospitals 15-20  cts.  per  cu.  ft. 

These  costs  include  the  building  complete,  omitting  power,  heat, 
light,  elevators,  and  decorations  or  furnishings. 

In  "Reinforced  Concrete  in  Factory  Construction,"  published 
in  1907,  by  the  Atlas  Portland  Cement  Co.,  it  is  stated  that  the  cost 
of  reinforced-concrete  factories  finished  complete  with  heating, 
lighting,  plumbing,  and  elevators,  but  without  machinery,  may 
run  under  actual  conditions  from  8  to  12  cents  per  cubic  foot  of 
total  volume,  measured  from  footings  to  roof.  The  former  price 
may  apply  where  the  building  is  erected  simply  for  factory  purposes 
with  uniform  floor  loading,  symmetrical  design,  which  permits  the 
forms  to  be  used  over  and  over  again,  and  with  materials  at  moderate 
prices.  The  higher  price  will  usually  cover  buildings  located  in 
restricted  districts,  where  the  appearance  both  of  the  exterior  and 
interior  must  be  pleasing.  The  cost  does  not,  however,  in  either 
case  include  interior  plastering  or  partitions. 

Cost  of  Concrete  Residences. — The  following  comparative 
building  costs  of  different  systems  of  buildings  are  based  upon  an 
average  frame  dwelling  costing  $10,000  complete,  located  in  the 
vicinity  of  New  York : 

(a)  $10,000  Frame. 

(&)  $11,000  Brick  outside  walls,  wooden  inside. 

(c)  $10,250  Stucco  on  expanded  metal,  wooden  inside. 

(d)  $10,500  Hollow  terra  cotta  blocks  stuccoed,  wooden  inside. 

(e)  $12,000  Hollow  blocks  stuccoed:   fireproof  throughout  except  roof. 

(/)   $14,000  Hollow  terra  cotta  block  walls  faced  with  brick,  fireproof  floors  and  roof. 
(g)   $15,000  Brick  walls,  fireproof  floors  and  roof. 

[411] 


Handbook  for  Cement  and  Concrete  Users 


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[412] 


Cost  of  Concrete  Work 


The  above  figures  are  based  on  an  average  taken  from  two 
architects  and  two  builders,  who  have  had  experience  with  the 
methods  of  construction  designated  and  have  been  compiled  by 
The  National  Fireproofing  Co. 

Cost  of  Constructing  Concrete  Sewers. — In  Engineering 
News,  for  Feb.  3,  1910,  Mr.  Frederick  R.  Charles,  City  Engineer, 
Richmond,  Ind.,  gives  the  following  table,  showing  the  costs  per 
lineal-  foot  for  materials  and  labor  employed  in  placing  the  concrete 
for  sewers  ranging  from  42  to  54  ins.  in  diameter,  which  were  re- 
cently constructed  in  Richmond,  Indiana: 

Cost  per  Linear  Foot  of  Concrete  Sewers  at  Richmond,  Indiana. 

Diameter  of  sewer 54  ins.  48  ins.  42  ins. 

Thickness  of  shell    5  ins.  5  ins.  4  ins. 

Total  cost,    exclusive     of     machinery, 

and   superintendence    $i-349          $1.083  $0.911 

In  Engineering  Record  for  April  4,  1908,  the  cost  of  building  a 
53  X  54  in.  arch  sewer  with  cement  at  $1.53  per  bbl.,  sand  at 
$0.50  and  broken  stone  at  $1.10  per  cu.  yd.,  is  stated  to  be  at  the 
rate  of  $2.97  per  lineal  foot  or  $8.02  per  cu.  yd.  of  concrete. 

Data  on  Cost  of  Concrete  Pipe. — The  following  figures  are  given 
in  the  March  Bulletin  of  the  U.  S.  Reclamation  Service  for  1908, 
and  relate  to  the  cost  per  lin.  ft.  of  constructing  concrete  pipe. 

Cost  of  cement,  $3.05  per  bbl.;  of  sand,  $1.40  per  cu.  yd.;  and 
of  labor,  $5.00  per  day  for  foremen;  $3.00  per  day  each  for  two 
men;  and  $2.75  per  day  each  for  two  men.  The  concrete  was 
made  of  i  part  cement  and  3  parts  sand.  The  unit  costs  were 
as  follows: 


Diameter  of  Pipe. 
Inches. 

Thickness. 
Inches. 

Weight  per 
Linear  Foot. 
Lbs. 

Number  of  Feet 
Made. 

Cost  per  Foot. 

12 

I  H 

56 

144 

So-  25 

18 

IK 

94 

248 

•37 

24 

2 

143 

56 

•57 

36 

3 

366 

54 

i-i5 

Cost  of  Large  Concrete  Pipes. — In  the  Reclamation  Record  for 
June,  1908,  the  cost  of  constructing  63  1/2  in.  concrete  pipe  at 
Ballantine,  Montana,  is  given  at  $6.90  per  lin.  ft.,  and  the  unit  cost 
at  $11.64  per  cu.  yd. 


Handbook  for  Cement  and  Concrete  Users 

Cost  of  Reinforced-Concrete  Culverts. — In  Engineering-Con- 
tracting for  July  i,  1908,  the  cost  of  constructing  a  7 -foot  reinforced- 
concrete  box  culvert  with  flat  roof  slabs  at  Huntley,  Montana,  is 
given  at  $17.41  per  cu.  yd.;  while  the  cost  of  the  steel  was  $0.0327 
per  pound  in  place. 

Cost  of  Concrete  in  Bridge  Piers. — The  following  costs  for 
materials  and  labor  used  in  placing  concrete  used  to  construct  the 
piers  and  abutments  of  the  Chattahoochee  River  Viaduct  near 
Atlanta,  Ga.,  in  1907,  were  given  by  Mr.  John  W.  Ash  in  the 
Engineering  Record,  for  Aug.  29,  1908.  These  costs  do  not  include 
excavation  or  cofferdam  construction: 

Total  cost  of  materials $20,555.83 

Total  cost  of  labor , 4,515.39 


5,024  cu.  yd $25071.22    =  $4.99  per  cu.  yd. 

The  total  cost  of  the  work,  including  excavation,  cofferdams,  pile 
driving,  etc.,  was  about  $45,000. 

Cost  of  Reinforced-Concrete  Bridges. — The  approximate  total 
cost  of  reinforced-concrete  highway  bridges,  including  excavation, 
falsework,  and  all  other  charges,  is  from  $2.50  to  $10.00  per  sq.  ft. 
of  roadway  area. 

The  following  are  actual  costs  of  recently  built  structures: 

Mulbury  Street  reinforced-concrete  viaduct,  Harrisburg,  Pa., 
which  is  1,841  ft.  long  and  consists  of  19  arches,  varying  in  span 
from  36  to  93  ft.  in  the  clear,  cost  $2.60  per  sq.  ft.  of  roadway  area. 
This  bridge  is  fully  described  in  Engineering  News,  Jan.  13,  1910. 

Two-span  highway  bridge  near  Carlisle,  Pa.,  consisting  of  two 
62  ft.  9  in.  arches,  was  built  in  1909  at  a  cost  of  $2.35  per  sq.  ft. 
of  bridge  floor.  This  structure  is  described  in  Engineering  Record 
for  Feb.  19,  1910. 

In  his  paper  on  "  Cost  of  Concrete  Bridges,"  presented  to  the 
National  Association  of  Cement  Users  in  1907,  Mr.  Henry  H. 
Quimby,  Engineer  of  Bridges  of  Philadelphia,  said  in  part : 

"Of  18  concrete  arch  bridges  recently  built  in  Philadelphia,  the 
concrete  price  spread  upon  the  span  area — the  clear  span  by  the 
width — varies  from  $3.11  to  $9.74  per  sq.  ft.  The  average  of  the 
lot  was  $6.25  per  sq.  ft.  of  span  area,  most  of  them  being  single-span 
bridges  with  long  wings,  and  all  being  highway  bridges  designed  to 


Cost  of  Concrete  Work 

carry  loads  of  40  tons  on  two  axles  20  ft.  apart.  All  have  ornamental 
concrete  balustrades  and  washed  granolithic  surfaces  and  paved 
decks,  with  electrical  conduits  and  manholes,  and  water  pipe  and 
sewer  well-holes,  and  some  have  pretty  deep  foundations.  If  the 
whole  contract  price  be  set  against  the  yardage  of  the  concrete  in  the 
structure,  the  unit  costs  vary  from  $8.50  to  $11.25  per  cu.  yd., 
averaging  $9.75." 

Mr.  Quimby  also  states  that  in  several  instances  where  oppor- 
tunities for  fair  comparison  occurred,  steel  plate-girder  bridges 
would  have  cost  25  per  cent,  more  than  the  reinforced-concrete 
bridges,  which  were  constructed.  A  real  money  value  also  attaches 
to  the  superior  beauty  and  attractiveness  of  a  decorative  arch  over 
that  of  a  purely  utilitarian  structure. 

Cost  of  Constructing  Piers  on  Concrete  Piles. — Two  piers  built 
at  Brunswick,  Ga.,  in  1906,  one  500  ft.  long  and  140  ft.  wide;  the 
other  900  ft.  long  and  140  ft.  wide,  both  constructed  on  concrete 
piles,  cost  $1.40  per  sq.  ft.  The  piers  are  described  in  Engineering 
News,  May  20,  1909.  In  a  similar  pier  built  at  Charleston,  S.  C., 
described  in  the  same  issue,  the  cost  was  $2.60  per  sq.  ft. 

Cost  of  Concrete  Piles. — In  a  dike  recently  constructed  on  the 
Missouri  River  at  St.  Joseph,  Mo.,  and  described  in  Engineering 
News,  Feb.  18,  1909,  Cap.  Edw.  H.  Schulz,  Corps  of  Engineers, 
U.  S.  A.,  gave  the  following  data: 

Total  piles  driven,  36;  total  lin.  ft.,  1,457;  length  of  piles,  32 
to  50  ft.;  penetration,  average,  21  ft.  Total  cost,  $1977.21  or  $1.36 
per  lin.  ft.  of  pile. 

Cost  of  Concrete  Trestles. — The  average  cost  of  concrete  trestles, 
used  to  replace  similar  timber  structures  on  the  Chicago,  Burlington 
and  Quincy  Railroad,  is  given  by  Mr.  C.  H.  Cartlidge,  bridge  en- 
gineer for  the  railroad,  in  Engineering  Record,  April  23,  1910. 

These  trestles  vary  in  length  from  100  to  over  1,000  ft.  The 
bents  are  spaced  from  14  to  16  ft.  c.  to  c.  Each  bent  consists  of 
six  i6-in.  rolled  piles  spaced  2  .ft.  4  in.  on  centres.  The  cap  is  2  1/2 
ft.  wide,  3  ft.  3  in.  deep,  and  14  ft.  long.  The  floor  is  14  ft.  wide, 
made  up  of  two  solid  reinforced-concrete  slabs  each  7  ft.  wide  and  i 
ft.  ii  in.  in  minimum  thickness  for  a  slab  of  i6-ft.  span.  Parapets 
6  in.  high  are  cast  on  the  slab  to  retain  the  ballast. 

The  cost  of  the  trestles  is  said  by  Mr.  Cartlidge  to  vary  from 

[4i5] 


Handbook  for  Cement  and  Concrete  Users 

$20.00  to  $45.00  per  lineal  foot.  For  estimating  purposes  a  cost  of 
$30.00  plus  a  constant  of  $300.00  was  ample  for  any  design. 

Cost  of  Reinforced-Concrete  Poles. — In  Engineering-Contracting 
for  Feb.  26,  1908,  the  cost  of  constructing  reinforced-concrete  poles 
30  ft.  long,  and  6x6  ins.  in  sectional  area  at  the  top,  and  10  X  10 
ins.  at  the  base,  is  stated  to  be  $7.45. 

The  cost  of  erecting  a  pole  of  this  size  is  said  to  be  $1.00  when 
proper  equipment  is  provided. 

In  the  March  1 1, 1908,  issue,  of  the  same  journal  the  following  cost 
data  for  reinforced-concrete  poles,  erected  at  Richmond,  Ind.,  is  given : 


Length. 
Feet.      , 

Top. 
Inches. 

Bottom. 
Inches. 

Cost. 

25 

6 

IO 

$6.71 

30 

6 

II 

8.63 

35 

6 

12 

u-45 

40 

7 

15 

I7-05 

45 

7 

16 

21.78 

50 

7 

17 

25-5o 

55 

7 

18 

31-93 

60 

7 

J9 

36.60 

Cost  of  Constructing  Concrete  Sidewalks. — The  following  data 
relates  to  the  cost  of  laying  cement  sidewalks  in  Chicago,  and  is 
condensed  from  a  paper  by  Mr.  N.  E.  Murray,  Superintendent  of 
Sidewalks,  for  Chicago,  111.,  which  was  printed  in  Engineering 
News,  Feb.  17,  1910. 

The  ordinary  concrete  sidewalk  gang  in  Chicago  is  usually 
composed  of  six  men,  paid  as  follows  (for  8  hours) :  i  finisher  at 
65  cts.,  $5.20;  i  helper  at  47  1/2  cts.,  $3.80;  4  laborers  at  37  1/2 
cts.,  $12.00;  total  $21.00.  Such  a  gang  will  lay  on  the  average 
600  sq.  ft.  per  day  of  5 -inch  cement  walk. 

The  cost  per  day  for  materials  and  labor,  including  the  cost  of 
filling  and  grading,  is  as  follows: 

Cinders  (allow  for  20  per  cent  shrinkage),  20.83  cu-  yds.  a*  5°  c*s< 

Base,  4%  ins.  (i:  2  H:  5) $10.42 

Cement,  9.77  bbls.  at  $1.20 $11.72 

Sand,  3.47  cu.  yds.  at  1.75 6.07 

Gravel,  6.85  cu.  yds.  at  1.50 10 . 28 

$28.07 


416] 


Cost  of  Concrete  Work 

Brought  forward  from  previous  page $38.49 

Wearing  coat,  Kins.  (2:3): 

Cement,  5.56 bbls.  at  $1.20 $6.67 

Sand,  1. 17  cu.  yds.  at  $1.75. 2  .04 

8.71 

Water,  at  i  mill  per  sq.  ft .60 

Labor,  one  gang  per  day 21 .00 

Use  of  tools,  waste  of  materials,  etc.,  at  2  per  cent i  .37 

Supt.  and  office  expenses  at  5  per  cent 3.51 

Profit  at  10  per  cent . 7 . 36 


Total  cost  per  day $81 .04 

Average  cost  13.51  cts.  per  sq.  ft. 

Cost  of  Concrete  Curb  and  Gutter. — The  cost  of  building  con- 
crete curb  and  gutter  is  about  40  cts.  per  lineal  foot,  including  ex- 
cavation, for  a  gutter  slab  24  ins.  wide,  and  a  curb  12  ins.  high,  both 
curb  and  gutter  being  laid  monolithic  in  7-foot  alternate  sections, 
with  a  3/4  in.  surface  coat  of  cement  and  sand. 

Cost  of  Concrete  Boundary  Monuments. — The  cost  of  building 
103  concrete  monuments  in  post  holes  five  feet  deep,  the  average 
sectional  area  being  8X8  ins.,  is  stated  by  Mr.  Leonard  Metcalf 
in  Engineering  Record,  for  Jan.  i,  1910,  as  averaging  $4.30  for  each 
monument. 

Cost  of  Constructing  Concrete  Silos.— Data  taken  from  Hoard's 
Dairyman,  for  June  19,  1908,  and  described  in  Engineering-Con- 
trading  for  Sept.  9,  1908. 

Cost  of  concrete  silo  10  ft.  in  diameter,  and  31  ft.  deep — 15  ft. 
in  ground  and  16  ft.  above. 

Materials,  $75.00;   labor,  $97.00.     Total,  $172.00. 

Cost  of  Constructing  Concrete  Roofs  for  Filters  and  Reservoir.— 
This  should  approximate  $6.00  per  cu.  yd.  In  Engineering  News 
for  April  7,  1910,  Mr.  Thomas  H.  Wiggin,  Assoc.  M.Am.  Soc. 
C.E.,  gives  data  on  the  design,  construction,  and  cost  of  44  different 
filters  and  reservoirs.  In  these  structures,  the  cost  of  constructing 
the  groined  arch  roofs  varied  from  $0.182  to  $0.61  cts.  per  sq. 
ft.,  depending  upon  the  span,  thickness,  and  other  conditions. 

Mr.  Wiggins  estimates  the  comparative  cost  of  plain  concrete 
groined  roofs  as  $0.25  and  reinforced-concrete  slab  roofs  as  $0.54 
per  sq.  ft. 

Cost  of  Concrete  Tunnel  Lining.— The  Gunnison  Tunnel, 
recently  completed  by  the  Reclamation  Service  near  Montrose, 
27  [417] 


Handbook  for  Cement  and  Concrete  Users 


Colo.,  is  the  largest  work  of  its  character  and  purpose.  This  tunnel 
has  a  width  of  about  n  ft.,  a  height  of  12  ft.,  and  a  length  of  31,000 
ft.  The  following  data  as  to  the  cost  of  lining  about  984  lin.  ft.  of 
arch  and  side  walls  with  plain  concrete  was  compiled  by  Mr.  F. 
W.  Hanna,  engineer  U.  S.  Reclamation  Service  and  published  in 
Engineering  Record,  May  30,  1908. 

The  rate  of  wages  was  for  foremen,  $5.00  per  day;    and  for 
laborers,  $3.04.     The  mixture  was  in  the  proportion  of  i  :  2  1/2:5. 

TABLE    SHOWING    COST   OP   CONCRETE    TUNNEL   LINING  IN  THE    GUNNISON 

TUNNEL 


Distribution  of  Cost. 

Total  Cost. 

Cost  per 
Linear  Foot. 

Cost  per 
Cubic   Yard. 

Superintendence 

187  ?o 

$0.203 

$O    212 

Placing  steel  forms  
Tearing  down  forms.    .    .                    

275.12 
288.80 

0-33° 
o  .  307 

Q-351 

O.  321 

Mixing  concrete 

•2Q^    ^2 

o  33I 

O    34.S 

Placing  concrete   

S8^.68 

o  .632 

o  .6^0 

Hauling  concrete                                

218  02 

0.236 

O.246 

Sand  and  gravel  at  $o  637  per  cu  yd 

70?    70 

o  8^0 

o  807 

Cement  delivered  at  $3  oo  per  barrel 

•77JQ      JC 

3CQ2 

37CO 

$5971.49 

$6.496 

$6.781 

During  the  period  in  question,  818  linear  feet  of  forms  were  put 
into  place  and  940  linear  feet  were  taken  down. 

Cost  of  Waterproofing. — Hot  coal-tar  and  felt.  Horizontal 
ist  ply — $2.00  to  $4.00  per  square  (100  sq.  ft.).  Additional — $1.50 
to  $2.50  per  square. 

Vertical,  add  10  per  cent  to  25  per  cent. 

Pressure  work,  i  ply  $4.00  to  $5.00  per  square.  Commercial 
asphalt  and  asphalt  felt,  add  15  per  cent  to  60  per  cent  per  ply; 
special  asphalts  and  felts,  add  30  per  cent  to  50  per  cent  per  ply; 
cold  process — felt  or  burlap,  same  as  commercial  asphalt;  asphalt 
mastic,  i  in.,  15  cts.  per  sq.  ft. 

Cement  waterproofing  compounds. — i  in.  on  floors,  J  in.  to  f  in. 
on  walls,  8  to  30  cts.  per  sq.  ft. 

Dampproofing  masonry  walls. — 2  coats  applied  in  place,  2  to  4 
cts.  per  sq.  ft. 

In  a  paper  presented  to  the  National  Association  of  Cement 

[418] 


Cost  of  Concrete  Work 

Users  in  1907,  Mr.  H.  Weiderhold,  Mgr.  Vulcanite  Paving  Co., 
Philadelphia,  Pa.,  states  that  the  cost  of  asphalt  mastic  for  water- 
proofing in  the  vicinity  of  New  York,  when  laid  in  i-inch  layers,  will 
range  from  15  to  25  cts.  per  sq.  ft. 

In  Engineering  Record  for  Oct.  31,  1908,  is  given  the  following 
cost  data  for  waterproofing  concrete-covered  bridge  floors  with  felt 
cemented  together  with  Hydrex  compound,  as  used  by  the  Central 
R.  R.  of  New  Jersey,  on  their  through  girder  bridges. 

"The  work  per  square  of  100  sq.  ft.  required  1.66  hours  of  time 
for  a  foreman,  11.71  hours  water-proof ers'  time,  and  7.75  hours  of 
laborers'  time.  The  best  record  was  750  sq.  ft.  in  one  day  of  10  hrs., 
while  the  average  time  was  40  per  cent  longer.  The  materials  cost 
2of  cents,  and  the  labor  i  of  cents  per  sq.  ft.  for  a  five-ply  covering. 

Cost  of  Reinforced  Concrete  in  Dam  Construction.— The  Corbett 
Diversion  Dam  of  the  Shoshone  Irrigation  Project,  near  Cody, 
Wyoming,  is  of  the  reinforced-concrete  buttressed  type,  having  a 
deck  30  in.  thick  on  the  upper  side  with  a  slope  of  i  to  i.  This  deck 
rests  on  buttresses  two  feet  thick,  spaced  14  ft.  on  centres.  The 
following  data  as  to  the  unit  cost  of  concrete  placed  in  the  structure 
is  condensed  from  the  Reclamation  Record  of  August,  1907. 

Materials  and  engineering,  $5.00  per  cu.  yd. 

Contractors'  labor  and  plant  charges,  $10.00  per  cu.  yd. 

Placing  steel,  $.035  per  Ib. 

Cost  of  Rubble  Concrete. — In  Engineering-Contracting  for  Oct. 
7,  1908,  is  given  the  following  cost  data  for  placing  30,000  cu.  yds. 
of  concrete  in  a  rubble-concrete  dam  near  Chicago : 

Cost  per  Cubic  Yard 
Concrete  in  Place. 

Stone Sr  .  26 

Sand 0.46 

Cement 2.31 

Forms o .  62 

Mixing o  .58 

Placing o  .69 


Total $5 .92 

In  the  canvass  of  bids  opened  Aug.  6,  1907,  by  the  Board  of 
Water  Supply  of  New  York  City,  for  the  construction  of  the  Main 
Dams  of  the  Ashokan  Reservoir,  the  bid  submitted  by  Messrs. 

[419] 


Handbook  for  Cement  and  Concrete  Users 


Me  Arthur  Bros,  and  Winston,  who  received  the  contract,  was  as 
follows  for  concrete  construction: 


Description. 

Unit. 

Quantity. 

Price. 

Portland  Cement 

Barrels 

$1     5O 

Concrete  Masonry  

Cubic  Yards 

280  ooo 

400 

Cyclopean  Masonry  Class  A 

«           « 

4.75  OOO 

•7      AQ 

Cyclopean  Masonry,  Class  B  

«           « 

«;  <  ,000 

"?    QO 

Concrete  Blocks 

«                      11 

64  ooo 

1  1    5O 

Grout  of  Portland  Cement    . 

"     Feet 

5  ooo 

O    5O 

The  total  bid  on  all  of  the  estimated  quantities  for  this  work,  of 
which  concrete  represents  a  large  percentage,  amounted  to  $12,669,- 
775.00.  The  actual  unit  costs  to  the  contractor  for  concrete  may  be 
approximated  by  deducting  15  per  cent  from  each  item.  This 
represents  his  probable  profits  for  the  work. 

HEAVY  TRIANGULAR   POSTS. 


Materials. 

Cost. 

Number  of 
Posts. 

Cost  per 
Post. 

i  yard  of  rock  or  gravel 

$1    OO 

2O 

$  03  % 

i  yard  of  sand 

I    OO 

c8 

Ol  K 

i  barrel  of  cement  
3  two-ply  No.  12  wire  cables  (weight  i  Klbs.) 
2  men  for  one  hour  at  20  cents  per  hour  
i  boy  for  one  hour  at  15  cents  per  hour  

1.50 

.025  per  Ib. 
.40               | 

ir                    ( 

18 
i 

5 

.08  y, 

.Q\% 
.11 

Total  Cost  

2Q 

STRAIGHT  SQUARE  POSTS. 


i  yard  of  rock  or  gravel   

$1    OO 

2C 

$  04 

i  yard  of  sand  .    ... 

I    OO 

CQ 

02 

i  barrel  of  cement    . 

I    ^O 

16 

oo  K 

4  two-ply  No.  12  wire  cables  (weight  2  Y*  Ibs.) 
2  men  for  one  hour  at  20  cents  per  hour  
i  boy  for  one  hour  at  15  cents  per  hour  

.025  per  Ib 
.40               [ 
•*5               i 

i 

5 

.05  K 

.11 

Total  cost    

-J2  X 

Cost   of   Reinforced-Concrete   Fence   Posts. — The    above   data 
relative  to  the  cost  of  constructing  7-foot  reinforced-concrete  fence 

[420] 


Cost  of  Concrete  Work 

posts  was  published  in  Bulletin  403  of  the  U.  S.  Dept.  of  Agriculture, 
issued  May  21,  1910.  The  mixture  consists  of  i  part  of  cement,  2 
parts  of  sand,  and  4  parts  of  crushed  rock  or  screened  gravel;  a 
reinforcement  consisting  of  two  No.  12  smooth  fencing  wires  twisted 
into  a  cable  and  cut  to  the  necessary  length  at  the  factory;  concrete 
mixed  by  hand;  all  material  delivered  at  the  work,  and  all  labor  of 
men  and  teams  paid  for. 


[421] 


INDEX 


ABUTMENTS,  255,  264,  274 
Acid  for  bonding,  362 

treating  surfaces,  1 1 1 
Activity  of  cement,  18 
Aggregates 

sand,  gravel,  and  broken  stone,  36 

selected,  for  surface  finish,  112 
Alkali,  effect  of,  on  concrete,  31,  281 
Arches,  concrete,  261 

backfilling,  271 

centres  for,  268 

construction  of  arches,  271 

definitions  of  parts,  261 

design  of,  263 

kinds  of  arches,  262 

methods  of  failure  of,  263 
crushing,  263 
poor  foundations,  263 
rotation,  263 
sliding,  263 

reinforced  concrete  for,  265 
types  of,  265 

removing  centres,  269 

waterproofing,  370 
Architecture,  concrete,  3,  78 
Asphalt,  concrete,  27 

for  waterproofing,  353 
Atlas   Portland   Cement   Co.,    162,  163, 

184,  259,  279,  293,  300 

BANK  sand  and  gravel,  39,  5 1 
Batch  mixers,  53 
Beams  and  slabs 

bridges,  273 

design  of,  169,  195 

forms  for,  71 

in   factory  and  building  construction, 

223 
Blocks,  concrete,  118 

advantages  of,  119 

concrete  block  data,  134 

construction  details  for,  129 

cost  of,  130 


Blocks,  inspection  of,  397 
machines  for,  124 
making  the  block,  125 
dry  process,  125 
wet  process,  126 
facing,  126 
curing,   127 
coloring,  127 

manufacturing  processes,  121 
materials  for,  119 
objections  to,  131 
specifications  for,  135 
tests  for,  137,  138 
types  of,  121 

waterproofing  concrete  blocks,   128 
Blome  granitoid  pavement,  314 
Bonding  new  to  old  concrete,  362 
Bridges,  concrete 
advantages  of,  273 
arch  bridges,  265 
advantages  of,  266 
general  types  of,  265 
beam  and  girder  bridges,  273 
classes  of,  274 

beam  and  slab  bridges,  275 
girder  bridges,  276 
flat  slab  bridges,  275 
trusses,  277 
Building  construction 

advantages  of  concrete  for,  223 
construction  details  for,  224 
basement  floor,  227 
columns,  226 
floor  slabs,  224 
floor  system,  228 
layout,  229 
loading,  228 
roofs,  230 
shafting,     method     of    attaching, 

230 

stirrups,  225 
walls,  230 
Bumping  posts,  324 


[423] 


Index 


CAISSONS,  243 

Carving  surfaces,  115 

Castings,  ornamental  concrete,  139 

Cements,  5 

choice  of  cement,  15 

common  lime,  5,  16 

fat  lime,  5 

hydraulic  cement,  5,  8 

hydraulic  lime,  5,  6,  16 

natural  cement,  9,  15 

plaster  cements,  14 

Portland  cement,  n,  15 

puzzuolana,  7 

quick  lime,  5 

slacking,  5 

slag  or  puzzolan,  14,  1 6 

slaked  lime,  5 

testing,  20 

Cement  coatings  for  waterproofing,  366 
Centring,  268,  278 
Cess  pools  (see  Farm) 
Chenoweth  pile  (see  Piles) 
Cinder  concrete,  26 
Clinton  wire  cloth,  217 
Coal  pockets,  322 

Coal  tar  pitch  for  waterproofing,  353 
Coatings,  cement,  for  waterproofing,  366 
Color  of  cements,  18  . 

Coloring,  113 

blocks,  127 

sidewalks,  208 

stucco  (see  Plasters) 
Columbian  system,  221 
Columns 

design  of,  173,190 

forms  for,  69 

reinforcement  for,  216 

use  in  buildings,  226 
Compounds  for  waterproofing  (see  Water- 
proofing) 
Concrete,  26 

aggregates  for,  36 

architecture,  78 

consistency  of, 
dry,  29 

grout  or  liquid  concrete,  29 
medium  wet,  29,  58 
very  wet,  29,  58 

effect  of  various  agencies  on,  27 
aggregates,  28 


Concrete,  coloring  matter,  29 

gases,  alkali,  sewage,  31 

heat,  31 

sea  water,  31 

water,  29 
forms  for,  64 
inspection  of,  386 
kinds  of  concrete,  26 

asphalt  concrete,  27 

cinder  concrete,  26 

reinforced  concrete,  27 

rubble  concrete,  26 
mixing,  47 
placing,  58 
proportioning,  42 
strength  of,  33 
waterproofing  of,  344 
Concrete  structures,  etc. 
abutments  (see  Abutments) 
arches  and  arched  bridges,  261 
beams,  slabs,  and  columns,  169 
bridges,  265 
building  blocks,  118 
bulkheads  (see  Retaining  Walls) 
culverts,  289 
curbs  and  gutters,  310 
dams,  298 
on  the  farm,  332 

fence  posts  (see  Fence  Posts),  157 
foundations,  233 
"liquid"  or  grout,  378 
ornamental  concrete,  139 
pavements,  312 
pipes,  150 

railroad  construction,  317 
reinforced  concrete  (see  also  Reinforced 

Concrete),  27,  165 
reservoirs,  304 
residences,  82 
retaining  walls,  245 
sidewalks,  305 
surfaces,  treatment  of,   106 
systems  of  reinforcement  for,  215 
tanks,  294 

tiles  and  other  products,  131 
Counterforts  (see  Retaining  Walls) 
Cost  of  concrete  work,  400 

elements  of  cost,  materials,  handling, 

etc.,  401 
general  cost  of  main  classes,  400 


424] 


Index 


Cost  of  boundary  monuments,  417 

bridges,  414 

bridge  pier,  414 

building  blocks,  408 

culvert,  414 

curb  and  gutters,  417 

dams,  419 

fence  posts,  420 

forms,  412 

mortar,  407 

trowelling,  408 

paving  blocks,  409 

piles,  415 

poles,  416 

reinforced  concrete  buildings,  411 

removing  efflorescence,  409 

residences,  411 

rubble  concrete,  419 

sewers,  413 

sidewalks,  416 

silos,  417 

stucco,  410 

surfacing  sidewalks,   409 

tooling  surface,  409 

trestles,  415 

tunnel  lining,  417 

waterproofing,   418 
Cracking  of  surfaces,  115 
Culverts,  concrete,  289 
carrying  capacity,  289 
drainage  area,  289 
imperviousness  of,  292 
types  of  culverts,  290 

arch  culverts,  291 

box  culverts,  290 

pipe  culverts,  290 
Cyclopean  masonry,  26 

DAMS,  cost  of,  419 

pressures  on,  298 

reinforced  concrete  dams,  300 

small  dams,  298 
Dressing  of  forms  (see  Forms) 

EFFLORESCENCE,  366 

cost  of  removing,  409 
Elevators,  330 
Etching  with  acid,  in 
Expanded  metal,  217 


FAILURE,  methods  of,  263 

arches,  263 

retaining  walls,  246 
Farm,  concrete  on  the 

advantages  of,  332 

cess  pools,  337 

cisterns,  336 

dairy,  338 

drainage,  336 

fence  posts,  353 

hitching  posts,  333 

horse  blocks,  333 

silos,  341 

data  for  (see  Tables) 

stalls,  337 

troughs,  335 

useful  hints,  343 

watering  trough,  333 
Fence  posts,  157 

fastening  fences  to  posts,  162 

machines  for,  156 

manufacture  of,  156 

moulds  for,  155 

reinforcement  for,  161 
Fineness  of  cement,  19 
Finishing  concrete  surfaces,  106 
Fireproof  ness  of  concrete,  166 
Floors,  concrete,  228 
Forms  for  concrete,  64 

beam  and  slab  forms,  71 

centring,  73 

column  forms 

timber,  bolted,  and  clamped  forms, 
70 

cost  of,  76 

dressing  and  lubrication  of,  74 

panel  form,  69 

pressure  of  concrete  on,  73 

simple  braced  forms,  65 

special  forms,  73 

studding  and  matched  boards,  68 

time  to  move  after  placing,  75 

wire  and  bolted  forms,  66 
Formula  for  proportioning  concrete,  44 
Foundations 

caissons  and  cribs,  243 

concrete  footings,  235 

concrete  for,  235 

cost  of,  400 

importance  of,  233 

425] 


Index 


Foundations  in  poor  soils,  234 
piles  (see  Piles),  237 
requirements  in  construction  of,  234 
safe  loads  on,  233 

GASES,  effect  of,  on  concrete,  31 
Grout  or  liquid  concrete,  375 

machines  for  mixing,  377 

preparing  and  mixing,  375 

uses  of,  375 

for   bonding  new  and  old   concrete, 

384 

for  cementing  joints,  377 
for  concrete  under  water,  379 
for  consolidating  riprap,  378 
for  machine  shop,  384 
for  miscellaneous  purposes,  385 
for  paving  filler,  384 
for  stopping  leaks  and  seams,  382 
for  surface  finish,  383 
for  tunnel  linings,  380 
for  walks,  383 
Gypsum  cements,  94 

HANDMIXING      of     concrete     (see     also 

Concrete) 
Hennebique  pile,  239 

system  of  reinforcement,  218 

INSPECTION  of  concrete 
divisions  of  the  work,  386 
duties  of  inspector,  386 
inspection  of 

aggregates,  387 

blocks,  397 

castings,  397 

cement,  386 

forms,  390 

measuring,  388 

mixing,  388 

piles,  398 

placing  concrete,  393 

proportioning,  388 

reinforcement,  391 

removal  of  forms,  395 

sand,  387 

surface  finish,  396 

waterproofing,    348,  355,    362,    364, 

394 
Integral  method  of  waterproofing,  362 


Internal  stresses,  169 
Introductory,  i 

JOINTS,  cementing  with  grout,  377 

KAHN  system,  217 
Keene's  cement,  95 
Keying,  92 

LAITANCE,  29 

Laths  (see  also  Plaster),  100 

Lime  (see  Cements) 

Liquid   concrete   or  grout,   375 

Literature,  concrete,  3 

Loads  on  (see  article  in  question) 

Lubrication  of  forms  (see  Form),  74 

MACHINE  mixing  of  concrete   (see  also 

Mixing),  52 
Martin's  cement,  75 
Mechanics  of  the  beam,  195 
Melan  system,  221 

Membrane  method  of  waterproofing,  351 
Merrick  system,  221 
Mixing  concrete  by  hand  and  machine,  47 

(see  also  Inspection) 
Modelling  ornamental  concrete,  139 
Mortar,  5,  16,  46,  90 
Moulds 

for  concrete  blocks  (see  Blocks) 

for  fence  posts  (see  Fence  Posts) 

ornamental  concrete,  142 

for  tiles  and  pipes  (see  Pipes) 

glue,  146 

metal,  143 

plaster,  144 

sand,  147 

wooden,  143 
Mushroom  system,  220 

NATURAL  cements  (see  Cements) 

OILS,  effect  of,  on  concrete,  31 
Ornamental  concrete,  139 
methods  of  manufacture,  139 

modelling,  139 

moulding,  142 

PARAFFINE  for  waterproofing,  368 
Pavements  (see  Roads) 

426] 


Index 


Pebble  dark  finish,  108,  109 
Piers  and  abutments,  264 
Piles 

advantages,  237 

concrete,  237 

disadvantages,  238 

historical,  237 
Pipes  and  tiles 

advantages  of,  150 

data  and  costs  of,  156 

machines  for,  151 

manufacture  of,  152 

moulds  for,  151 

reinforced  concrete  pipes,  154 
Placing  concrete,  58 

(see  also  Inspection) 
Plasters  and  plastering,  90 

cement  plasters,  14 

gypsum  plasters,  95 

Keene's,    Martin's,     and    Parian    ce- 
ments, 95,  96 

plaster  of  Paris,  95 

lime  plasters,  90 

plastering  interior,  91 

brown  coat,  92 

exterior  lathing  and  plastering,  100 

finishing  coat,  93 

Portland    cement    plasters   or    stucco, 
96 

scratch  coat,  91 

applications  of  stucco,  101 

materials  for  stucco,  105 

rules  for  metal  lath,  99 

specifications  for  laths,  98 
Platforms,  319 
Pneumatic  caissons,  243 
Poles,  concrete,  328 
Portland  cement  (see  Cement) 
Power  houses,  320 
Precautions  and  rules    for  mixing    (see 

also  Rules,  etc.),  56>  356>  364,  386 
Pressure  on  forms,  73 

hydrostatic,  299 

of  earth,  259 
Processes  of  manufacture  (see  article  in 

question) 

Properties  of  cements,  18 
Proportioning  materials  for  concrete,  42 

(see  also  Inspection) 
Protection  of  concrete  after  placing,  60 


Protection  of  waterproofing  (see  Water- 
proofing) 
Puzzuolana  (see  Cements) 

RAILROAD  construction,  concrete  in 

ash-handling  plants,  322 

bridges  and  trestles,  318 

bumping  posts,  324 

coal  and  sand  pockets,  322 

docks,  329 

foundations,  317 

grain  elevators,  330 

piers  and  abutments,  318 

pits,  324 

platforms,  319 

posts  and  fences,  327 

power  houses,  320 

railroad  shops,  321 

retaining  walls,  318 

roadbed,  327 

round  houses,  323 

signal  towers,  320 

stations  and  train  sheds,  319 

storage  reservoirs,  329 

telegraph  poles,  328 

ties,   325 

tunnels,  328 

turntables,  324 

Raymond  piles  (see  Piles),  241 
Reid,  Homer  A.,  300 
Reinforced  concrete,  165 

(see  also  Concrete) 

advantages,  165 

design  of  beams,  169,  195 

design  of  bond,  188,  209 

design  of  columns,  173,  190 

design  of  slabs,  178 

design  of  stirrups,  187 

materials  for,  167 

rules  for  design  of  beams,  173,  175 

rules  for  design  of  columns,  173,  190 

specifications  for,  210 

systems  of  reinforcement,  213 
(see  also  Systems) 

tables  for  use  in  design  (see  Tables) 
Removal  of  forms  (see  Forms) 
Requirements  for  cement,  23 

natural  cement,  24 

Portland  cement,  25 
Reservoirs,  concrete,  304 


427 


Index 


Residences,  concrete,  82 
architectural  features  of,  86 
concrete  block  residences,  83 
cost  of  concrete  residences,  89 
Edison  cast  concrete  house,  86 
kinds  of  concrete  residences,  83 
monolithic  residences,  84 
reinforced  concrete,  85 
surface  finishes  for  block  residences,  83 
stucco  residence,  84 
Retaining  walls 
appearance  of,  251 
design  of,  245 
drainage  of,  254 
earth  pressures  on,  246 
failures,  methods  of,  246 
bulging,  247 
overturning,  246 
sliding,  246 
foundations  for,  253 
land  ties  for,  254 
relieving  arches  for,  254 
types  of,  248 

gravity  walls,  248 
design  of,  248 

reinforced  concrete  walls,  249 
without  counterforts,  250 
with  counterforts,  251 
restrained,  252 
construction  of,  252 
Riprap,    consolidating    with    grout    (see 

Grout) 

Roadbeds,  327 

Roads  and  pavements,  concrete,  310 
patented  pavements,  314 
Blome  granitoid,  314 
Hassan  pavement,  315 
Roebling  system,  219 
Rough  cast  finish,  108 
Round  houses,  323 
Rubble  concrete,  26 
Rules  for  concrete  workers  (see  Inspec- 
tion) 


SAND  for  concrete,  36 

broken  stone  for  concrete,  39 
gravel  for  concrete,  40 

Scouring,  92,  93 

Screeds,  92 

Scrubbing  surfaces,  no 


Seams,  grouting  (see  Grout) 

Selected  aggregates  for  surface  finish,  112 

Sea  water,  effect  of,  on  concrete,  3 1 

Sewage,  effect  of,  on  concrete,  31 

Sewers,  concrete,  281 

Sidewalks,  concrete,  305 

advantages  of,  305 

coloring,  308 

construction  of,  306 
sub-base,  306 
base,  306 
wearing  surface,  307 

dimensions  of  (see  Tables) 

forms  for,  306 

materials  for,  305 

protecting,  308 

tools  and  equipments,  306 
Signal  towers,  320 
Silos  (see  Farm) 
Slab  bridges  (see  Bridges),  266 
Slacking  (see  Lime) 
Slag  cements  (see  Cements) 
Slap-dash  finish,  108 
Smooth -float  finish,  108 
Soundness  of  cement,  18 
Specifications  for  concrete  blocks,  135 
Specifications    for    design    of   reinforced 

concrete,  210 
Specifications  for  lathing  and  plastering, 

98 
Specifications      for     waterproofing     (see 

Waterproofing) 
Strength  of  cement,  19 
Strength  of  concrete,  33 
Stresses  in  reinforced  concrete 

tension,    compression,  shear,  bending, 

169,  170 

Stucco  and  its  application,  101-104 
Stucco  and  stuccoing  (see  Plasterers  and 

Plastering) 

Stucco  finishes  (see  Surface) 
Surface  coatings  for  waterproofing,  366 
Surfaces 

artistic  treatment  of  concrete,  106 

facing  with  mortar,  109 

imperfections  in  concrete,  106,  115 

methods  of  finishing,  107 

mosaics,  carving,  etc.,  115 

panelling,  114 

scrubbing  and  washing,  no 

[4»8] 


Index 


Surfaces,  selected  aggregates,  112  TABLES  : 

spading  and  trowelling,  158  xm. 

stucco  surfaces,  108  xrv. 

pebble  dash,  108,  109 

rough  coat,  108  xv. 

slap  dash,  108,  109 

smooth  float  finish,  108  xvi. 

tinting  and  coloring,  113 

tooling,  112  XVI  A. 

Surfaces,  cost  of  finishing,  409 

Systems  of  reinforcement,  215  xvil. 

rods  and  bars,  215 

wire,  216  xvni. 

expanded  metal,  217 

spiral  reinforcement  for  columns,  216  xix. 

special  systems,  216  xx. 

expanded  metal,  217 

Clinton  wire  cloth,  217  xxi. 

Kahn  system,  218  xxii. 

Hennebique,  218 

Hinchman-Renton,  218  xxni. 

Roebling,  219 

Turner,  Mushroom,  220  XXIV. 

Merrick,  221 

Melan,  221  xxv. 

Columbian,  221 

Unit,  222  xxvi. 

TABLES:  xxvn. 

I.  Outline  of  process  of  manu- 
facture   of    hydraulic    ce-  xxvm. 
ments,   10 
II.  Ingredients  in  one  cubic  yard  xxix. 

of  concrete,  45 
in.  Materials  for  one  cubic  yard  XXX. 

of  mortar,  46 
iv.  Materials  for  two-bag  batch  xxxi. 

of  concrete,  52 
v.  Bank    sand    and    gravel    re-  xxxn. 

quired  for  two-bag  batch,  53 
vi.  Pressure  on   forms   produced  xxxm. 

by  concrete,  74 

vn.  Sizes  of  metal  laths,  98  xxxiv. 

vni.  Quantities    for     100     square 

yards  of  laths,  98  xxxv. 

ix.  Area  covered  by  mortar,  105 
x.  Materials    for   coloring   mor-  xxxvi. 

tars,  114 

xi.  Concrete  block  data,  134  xxxvu. 

xii.  Hollow  spaces  in  blocks,  137 

[429] 


Data  for  concrete  tile,  156 

Quantity  of  materials  for 
fence  posts,  162 

Quantity  of  materials  for  cor- 
ner posts,  163 

Data  for  design  of  reinforced 
concrete  beams,  .176 

Co-efficients  for  design  of  rein- 
forced concrete  beams,  204 

Depths  of  beams  and  squares 
of  same,  181 

Weight  of  reinforced  concrete 
beams,  and  cost,  182 

Properties  of  steel  bars,  183 

Dimensions  of  reinforced  con- 
crete beams,  184 

Allowable  loads  on  floors,  229 

Earth  pressures  on  retaining 
walls,  259 

Dimensions  for  basement 
walls,  259 

Dimensions  for  gravity  re- 
taining walls,  260 

Dimensions  and  quantities  for 
slab  bridges,  279 

Amount  of  materials  for  arch 
culverts,  293 

Spacing  of  rods  in  concrete 
tanks,  296 

Spacing  of  rods  in  concrete 
tanks,  297 

Dimensions  of  circular  tanks, 
297 

Hydrostatic  pressures  at  vari- 
ous depths,  299 

Dimensions  for  small  dams 
and  materials  for  same,  300 

Dimensions  for  concrete  side- 
walks, 309 

Materials  for  concrete  side- 
walks, 309 

Offsets  for  crowning  streets, 

3i5 

Data  for  reinforced  concrete 
silos,  342 

Number  of  ply  ,and  thickness 
of  waterproofing,  352 

Outline  of  modern  water- 
proofing processes,  370 


Index 


TABLES : 

xxxvui.  Cost  of  forms    and  concrete 

in  buildings,  412 
Tanks,  concrete,  294 
Testing  cement,  20,  21 
Tiles,  concrete,  131 
Tremie   for   depositing    concrete    under 

water,  62 
Troughs,  334 
Trowelling,  93,  94,  108 
Tunnel  lining,  grout  for  (see  Grout) 
Turntables,  324 
Turner  mushroom  system,  220 

UNIT  system,  222 

VAN  DEERLIN,  R.,  on  concrete  architec- 
ture, 78 

Voids  in  concrete,  42 
Volume  of  barrel  of  cement,  43 

WATER  for  tempering  cement,  31 
Waterproofing,  cost  of,  374 
importance  of  inspection,  348 
general  principles  to  be  followed,  349 
method  of  conducting  the  work,  346 
work  under  contract,  346 
work  not  under  contract,  347 
modern  methods  of  waterproofing,  350 
integral  method,  359 

addition  of  materials  to  the  con- 
crete, 360 

compounds  employed,  361 
powders,  361 
waterproof  cements,  361 


Waterproofing  liquids,  361 

combinations,  361 
membrane  method 

applications  of  materials,  306 
continuity  of  work,  357 
preparation  of  surfaces,  356 
protection  of  work,  358 
materials  for,  351 
scope  and  applicability  of,  350 
specifications  for  materials,  353 
asphalt,  350 
asphalted  felt,  355 
coal    tar  pitch,   properties  and 

tests,  353 
necessity  for,  344 
surface  coatings,  366 
applicability  of,  366 
bituminous  process,  369 
cement  grouting  processes,  369 
materials  for,  366 
paraffine,  cold  process,  368 
pataffine,  hot  process,  368 
Sylvester  process,  367 
workmanship,  370 
rules  for  applying  coatings,  364 
application  of  coatings,  365 
preparation  of  coating,  364 
preparation  of  surface,  364 
tabular  outlines  of  modern  processes, 

37i 

waterproof  cement  coatings 
bond,  362,  363 
continuity,  363 
homogeneity  of  work,  363 
soundness,  363  -^J^ 


[430] 


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